Fix branch deletion after failed reconfig

Normally when a branch is deleted, we delete the cached data for
that branch and perform a partial ("tenant") reconfiguration.  However,
there are two caches of configuration for each project -- the full
cache, and the per-branch cache.  We were not deleting the per-branch
cache, so if the tenant reconfiguration failed, the per-branch cache
would still contain the deleted branch.

Also, on full reconfiguration, we update the per-branch cache, however,
we never deleted branches from the cache in that case, so even a full
reconfiguration would be unable to clear that cache.  This is fixed
as well.

Change-Id: Ia9c17238ef0e42609e3de304af9c0c4588c72995

tests/fixtures/config/branch-deletion/git/common-config/playbooks/base.yaml

@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []

tests/fixtures/config/branch-deletion/git/common-config/zuul.yaml

@@ -0,0 +1,17 @@
+- pipeline:
+    name: check
+    manager: independent
+    trigger:
+      gerrit:
+        - event: patchset-created
+    success:
+      gerrit:
+        Verified: 1
+    failure:
+      gerrit:
+        Verified: -1
+
+- job:
+    name: base
+    parent: null
+    run: playbooks/base.yaml

tests/fixtures/config/branch-deletion/git/org_project/zuul.yaml

@@ -0,0 +1,4 @@
+- project:
+    name: org/project
+    check:
+      jobs: []

tests/fixtures/config/branch-deletion/git/org_project1/zuul.yaml

@@ -0,0 +1,3 @@
+- project:
+    check:
+      jobs: []

tests/fixtures/config/branch-deletion/main.yaml

@@ -0,0 +1,10 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+        untrusted-projects:
+          - org/project
+          - org/project1
+