[CI] Replace deprecated regex and remove Centos8

Latest Zuul drops the following warnings:

  All regular expressions must conform to RE2 syntax, but an
  expression using the deprecated Perl-style syntax has been detected.
  Adjust the configuration to conform to RE2 syntax.

  The RE2 syntax error is: invalid perl operator: (?!

This patch replaces the 'irrelevant-files' to 'files' with explicitly
listing the pattern which files should be the tests run against.

NOTE(elod.illes): this patch is extended with the removal of CentOS 8
Stream based jobs as that OS is End of Life, hence removed from
available nodesets.

Change-Id: If287e800fb9ff428dbe6f9c4c046627f22afe3df
(cherry picked from commit 9b77bae8a32ff41712b96bb6a67c7eacae45a4c9)
(cherry picked from commit 8223e6a7c429441c28178316e455767a66d3e8f8)
(cherry picked from commit 510a27ba36fc47309308228bc45b5b9ea6ba695b)
(cherry picked from commit 197b14d7659252c62b7436bcdd2a9b8c8b470771)
(cherry picked from commit ffc252eeae01f4829a92a0549b47fb9e4175c2da)

.zuul.yaml

@@ -197,24 +197,11 @@
     parent: devstack-tempest
     description: |
       Run tempest compute API tests using LVM image backend. This only runs
-      against nova/virt/libvirt/* changes.
-    # Copy irrelevant-files from nova-dsvm-multinode-base and then exclude
-    # anything that is not in nova/virt/libvirt/* or nova/privsep/*.
-    irrelevant-files:
-      - ^(?!.zuul.yaml)(?!nova/virt/libvirt/)(?!nova/privsep/).*$
-      - ^api-.*$
-      - ^(test-|)requirements.txt$
-      - ^.*\.rst$
-      - ^.git.*$
-      - ^doc/.*$
-      - ^nova/hacking/.*$
-      - ^nova/locale/.*$
-      - ^nova/tests/.*$
-      - ^nova/test.py$
-      - ^releasenotes/.*$
-      - ^setup.cfg$
-      - ^tools/.*$
-      - ^tox.ini$
+      against nova/virt/libvirt/*, nova/privsep/* and .zuul.yaml changes.
+    files:
+      - ^nova/virt/libvirt/.*$
+      - ^nova/privsep/.*$
+      - .zuul.yaml
     vars:
       # We use the "all" environment for tempest_test_regex and
       # tempest_exclude_regex.
@@ -253,22 +240,11 @@
     # NOTE(chateaulav): due to constraints with no IDE support for aarch64,
     # tests have been limited to eliminate any items that are incompatible.
     # This is to be re-evaluated as greater support is added and defined.
-    irrelevant-files:
-      - ^(?!.zuul.yaml)(?!nova/virt/libvirt/)(?!nova/objects/)(?!nova/scheduler/).*$
-      - ^api-.*$
-      - ^(test-|)requirements.txt$
-      - ^.*\.rst$
-      - ^.git.*$
-      - ^doc/.*$
-      - ^nova/hacking/.*$
-      - ^nova/locale/.*$
-      - ^nova/policies/.*$
-      - ^nova/tests/.*$
-      - ^nova/test.py$
-      - ^releasenotes/.*$
-      - ^setup.cfg$
-      - ^tools/.*$
-      - ^tox.ini$
+    files:
+      - ^nova/virt/libvirt/.*$
+      - ^nova/objects/.*$
+      - ^nova/scheduler/.*$
+      - .zuul.yaml
     vars:
       tox_envlist: all
       tempest_test_regex: ^tempest\.(api\.compute\.servers|scenario\.test_network_basic_ops)
@@ -632,11 +608,12 @@
         - nova-ceph-multistore:
             irrelevant-files: *nova-base-irrelevant-files
         - neutron-linuxbridge-tempest:
-            irrelevant-files:
+            files:
               # NOTE(mriedem): This job has its own irrelevant-files section
               # so that we only run it on changes to networking and libvirt/vif
               # code; we don't need to run this on all changes.
-              - ^(?!nova/network/.*)(?!nova/virt/libvirt/vif.py).*$
+              - ^nova/network/.*$
+              - nova/virt/libvirt/vif.py
         - nova-live-migration
         - nova-live-migration-ceph
         - nova-lvm
@@ -680,11 +657,6 @@
         - barbican-tempest-plugin-simple-crypto:
             irrelevant-files: *nova-base-irrelevant-files
             voting: false
-        - tempest-integrated-compute-centos-8-stream:
-            irrelevant-files: *nova-base-irrelevant-files
-        - tempest-centos8-stream-fips:
-            irrelevant-files: *nova-base-irrelevant-files
-            voting: false
     gate:
       jobs:
         - nova-live-migration
@@ -697,11 +669,12 @@
         - nova-ceph-multistore:
             irrelevant-files: *nova-base-irrelevant-files
         - neutron-linuxbridge-tempest:
-            irrelevant-files:
+            files:
               # NOTE(mriedem): This job has its own irrelevant-files section
               # so that we only run it on changes to networking and libvirt/vif
               # code; we don't need to run this on all changes.
-              - ^(?!nova/network/.*)(?!nova/virt/libvirt/vif.py).*$
+              - ^nova/network/.*$
+              - nova/virt/libvirt/vif.py
         - tempest-integrated-compute:
            irrelevant-files: *policies-irrelevant-files
         - nova-grenade-multinode:
@@ -710,8 +683,6 @@
             irrelevant-files: *nova-base-irrelevant-files
         - openstacksdk-functional-devstack:
             irrelevant-files: *nova-base-irrelevant-files
-        - tempest-integrated-compute-centos-8-stream:
-            irrelevant-files: *nova-base-irrelevant-files
     experimental:
       jobs:
         - ironic-tempest-bfv: