Rely on ID/VERSION_ID to detect distro

REDHAT_SUPPORT_PRODUCT* are removed from recent
CentOS8.3 release[1], Let's use ID/VERSION_ID instead
which are available[2] and would serve our purpose.

[1] https://git.centos.org/rpms/centos-linux-release/c/2e3df0
[2] https://www.freedesktop.org/software/systemd/man/os-release.html

Also switch to train constraints and remove cap for Sphinx
and let it use from constraints which is 3.0.1 currently.

Change-Id: Ic10b461dde012e01de87eaf03745f17fbaf704e8
(cherry picked from commit 026d2feefd)

run_tests.sh

@@ -21,7 +21,7 @@ BRANCH=stable/train
 
 # Find OS version and release
 source /etc/os-release
-OS_NAME_VERS=${REDHAT_SUPPORT_PRODUCT}${REDHAT_SUPPORT_PRODUCT_VERSION}
+OS_NAME_VERS=${ID}${VERSION_ID}
 
 # We could want to override the default repositories or install behavior
 INSTALL_FROM_SOURCE=${INSTALL_FROM_SOURCE:-true}

test-requirements.txt

@@ -1,4 +1,4 @@
-sphinx>=1.6.2,<2.0.0  # BSD
+sphinx>=1.6.2  # BSD
 openstackdocstheme>=1.17.0  # Apache-2.0
 reno>=0.1.1 # Apache2
 stestr>=1.0.0 # Apache-2.0

tox.ini

@@ -10,7 +10,7 @@ setenv = VIRTUAL_ENV={envdir}
          LANGUAGE=en_US:en
          LC_ALL=C
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/train}
   -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/requirements.txt