TT#46500 Support triggering $debian_release/master branches

If we want to trigger a trunk build against e.g. Debian/buster we
might need to build certain projects against branch "buster/master",
instead of using the default "master" branch (which works fine for the
current Debian stable release AKA stretch, but might need
non-backwards compatible changes when building for the current Debian
testing release AKA buster ).

I identified two approaches to get there:

1) Statically extend the list of available branches which is available
   for selection in the "Version" drop down (which only provide "ignore"
   and "branch/master" until now).

   This could be done by something like:

| --- a/release_dashboard/utils/__init__.py
| +++ b/release_dashboard/utils/__init__.py
| @@ -14,6 +14,7 @@
|  # with this program.  If not, see <http://www.gnu.org/licenses/>.
|
|  from release_dashboard.models import Project
| +from release_dashboard.forms import rd_settings
|
|
|  def get_tags(projectname, regex=None):
| @@ -23,4 +24,8 @@ def get_tags(projectname, regex=None):
|
|  def get_branches(projectname, regex=None):
|      project, _ = Project.objects.get_or_create(name=projectname)
| -    return project.filter_branches(regex)
| +    branches = project.filter_branches(regex)
| +    for debian_release in rd_settings['debian_supported']:
| +        if debian_release != "auto":
| +            branches.append(debian_release + "/master")
| +    return branches

The disadvantage of this approach is, that we're listing all the
branches all the time, e.g. the very old "squeeze/master" is listed
even though it doesn't exist in any project as such.

2) Identify available branches and extend the regular expression
   which identifies the "master" branch by also looking for
   "$debian_release/master" branches, iterating over all supported
   Debian releases.

Since approach 2) doesn't polute the drop down for branch
selection so much, this is the solution I decided to use here.

JFTR, when testing locally against an unpopulated sqlite database (:=
db.sqlite3 file), then the relevant branches need to exist in the
release_dashboard_project table of the DB. To fake such data use
something like:

| root@16f2201e3229:/code# sqlite3 ./db.sqlite3
| SQLite version 3.16.2 2017-01-06 16:32:41
| Enter ".help" for usage hints.
| sqlite> update release_dashboard_project set json_branches = '[{"ref": "HEAD", "revision": "master"}, {"ref": "refs/heads/master", "revision": "fakedata"},
|         {"ref": "refs/heads/buster/master", "revision": "fakedata"}, {"ref": "refs/heads/stretch/master", "revision": "fakeeeeee"}]';

Change-Id: I5f24574e33ac80d1e92210ff5516dce4bf8fef76

release_dashboard/views/__init__.py

@@ -15,10 +15,19 @@
 
 import re
 from release_dashboard.utils import get_tags, get_branches
+from release_dashboard.forms import rd_settings
 
 regex_hotfix = re.compile(r'^mr[0-9]+\.[0-9]+\.[0-9]+$')
 regex_mr = re.compile(r'^mr.+$')
-regex_master = re.compile(r'^master$')
+
+# support "master" + "$supported_debian_releases/master" for branch selection,
+# e.g. for trunk builds when not everything might build against master
+debian_releases = []
+for debian_release in rd_settings['debian_supported']:
+    if debian_release != "auto":
+        debian_releases.append(debian_release)
+regex_master = re.compile(r'^master$|^(%s)/master$' %
+                          '|'.join(map(re.escape, debian_releases)))
 
 
 def _projects_versions(projects, regex=None,