Buildbot: support force building master and lts branches again

But without the option to specify the branch name.

master.cfg

@@ -58,22 +58,30 @@ from buildbot.schedulers import timed, forcesched
 c['schedulers'] = []
 
 
-def schedule_force_build(name):
+def schedule_force_build(name, branch):
     """
     Makes it possible to have "Force Build" for the given builder.
-    Makes sure only reasonabel subset of properties are exposed.
+    Makes sure only reasonable subset of properties are exposed.
     """
+    if branch != "":
+        branch_parameter = forcesched.FixedParameter(
+            name="branch",
+            default=branch,
+            hide=True)
+    else:
+        branch_parameter = forcesched.StringParameter(
+            name="branch",
+            label="Branch:",
+            default="custom-branch-name-here",
+            regex=r'^[a-zA-Z0-9][A-Za-z0-9\._-]*$')
+
     c['schedulers'].append(forcesched.ForceScheduler(
         name='force_' + name,
         buttonName="Force Build",
         builderNames=[name],
         codebases=[forcesched.CodebaseParameter(
                 codebase="blender",
-                branch=forcesched.StringParameter(
-                    name="branch",
-                    label="Branch:",
-                    default="custom-branch-name-here",
-                    regex=r'^[a-zA-Z0-9][A-Za-z0-9\._-]*$'),
+                branch=branch_parameter,
                 # Hide revision. We don't want to allow anyone to overwrite the
                 # master build with an older version. Could be added back once we
                 # have authentication.
@@ -148,10 +156,9 @@ def add_builder(c, name, platforms, factory, branch='',
                                                factory=f,
                                                tags=['blender']))
 
-            if branch == '':
-                schedule_force_build(builder_name)
-            else:
+            if branch != '':
                 schedule_nightly_build(builder_name, branch, hour, minute)
+            schedule_force_build(builder_name, branch)
 
 
 # common steps