Add default branch configuration option

Fixes: #1735

module_build_service/common/config.py

@@ -700,6 +700,11 @@ class Config(object):
                     "which buildrequires to automatically include. This can be overridden with "
                     "the xmd.mbs.default_modules_scm_url key in the base module's modulemd.",
         },
+        "default_branch": {
+            "type": str,
+            "default": "master",
+            "desc": "Denotes the default branch.",
+        },
         "uses_rawhide": {
             "type": bool,
             "default": True,

module_build_service/common/scm.py

@@ -71,8 +71,8 @@ class SCM(object):
         If url is not in the list of allowed_scm, an error will be raised.
 
         :param str url: The unmodified scmurl
-        :param str branch: The optional source control branch. This defaults to "master" when git
-            is used.
+        :param str branch: The optional source control branch. This defaults to the default_branch
+            config option when git is used.
         :param list allowed_scm: The optional list of allowed SCM URL prefixes
         :param bool allow_local: Allow SCM URLs that start with "file://"
         :raises: Forbidden or ValidationError
@@ -111,7 +111,7 @@ class SCM(object):
             if self.name.endswith(".git"):
                 self.name = self.name[:-4]
             self.commit = match.group("commit")
-            self.branch = branch if branch else "master"
+            self.branch = branch if branch else conf.default_branch
             self.version = None
             self._cloned = False
         else:

module_build_service/scheduler/submit.py

@@ -307,7 +307,7 @@ def format_mmd(mmd, scmurl, module=None, db_session=None, srpm_overrides=None):
             if not pkg.get_cache():
                 pkg.set_cache(conf.rpms_default_cache + pkgname)
             if not pkg.get_ref():
-                pkg.set_ref("master")
+                pkg.set_ref(conf.default_branch)
             if not pkg.get_arches():
                 for arch in conf.arches:
                     pkg.add_restricted_arch(arch)
@@ -323,7 +323,7 @@ def format_mmd(mmd, scmurl, module=None, db_session=None, srpm_overrides=None):
             if not mod.get_repository():
                 mod.set_repository(conf.modules_default_repository + modname)
             if not mod.get_ref():
-                mod.set_ref("master")
+                mod.set_ref(conf.default_branch)
 
         # It is possible to override the ref of RPM component using
         # the rpm_component_ref_overrides.

module_build_service/web/submit.py

@@ -122,7 +122,7 @@ def submit_module_build_from_yaml(
             '"module_name" parameter'
         )
     module_name = stream_or_packager.get_module_name() or def_name
-    module_stream = stream or stream_or_packager.get_stream_name() or "master"
+    module_stream = stream or stream_or_packager.get_stream_name() or conf.default_branch
     if module_name != stream_or_packager.get_module_name() or \
        module_stream != stream_or_packager.get_stream_name():
         # This is how you set the name and stream in the modulemd