Skip db preload on healtchcheck requests

Every web request triggers a db query to preload app header data. In case of health checks
we do not need to preload anything and can safely skip the @app.before_request.

Fixes #310

blockerbugs/controllers/main.py

@@ -35,11 +35,15 @@ from blockerbugs.models.update import Update
 from blockerbugs.models.release import Release
 from blockerbugs.controllers.forms import BugProposeForm
 
+HEALTH_CHECK_PATH = '/_health'
+
 main = Blueprint('main', __name__)
 
 
 @app.before_request
 def before_request():
+    if request.path == HEALTH_CHECK_PATH:
+        return
     g.milestones = Milestone.query.filter_by(active=True).order_by(Milestone.name).all()
     g.version = __version__
     g.version_date = misc.version_date()
@@ -279,7 +283,7 @@ def index():
     return display_current()
 
 
-@main.route('/_health')
+@main.route(HEALTH_CHECK_PATH)
 def get_health_check():
     """Endpoint for OpenShift pod health checks (liveness and readiness probes).