Add configurable limits for number of builds allowed under a namespace

We also support that limit being increased automatically once a successful billing charge has gone through

endpoints/test/test_building.py

@@ -0,0 +1,31 @@
+import pytest
+
+from data import model
+from endpoints.building import start_build, PreparedBuild, MaximumBuildsQueuedException
+
+from test.fixtures import *
+
+def test_maximum_builds(app):
+  # Change the maximum number of builds to 1.
+  user = model.user.create_user('foobar', 'password', 'foo@example.com')
+  user.maximum_queued_builds_count = 1
+  user.save()
+
+  repo = model.repository.create_repository('foobar', 'somerepo', user)
+
+  # Try to queue a build; should succeed.
+  prepared_build = PreparedBuild()
+  prepared_build.build_name = 'foo'
+  prepared_build.is_manual = True
+  prepared_build.dockerfile_id = 'foobar'
+  prepared_build.archive_url = 'someurl'
+  prepared_build.tags = ['latest']
+  prepared_build.subdirectory = '/'
+  prepared_build.context = '/'
+  prepared_build.metadata = {}
+
+  start_build(repo, prepared_build)
+
+  # Try to queue a second build; should fail.
+  with pytest.raises(MaximumBuildsQueuedException):
+    start_build(repo, prepared_build)