feat(buildtrigger): allow use to specify dockerfile

users can only specify the folder and the
  dockerfile must be names "Dockerfile" this allows
  users to specify the file and it can be called
  "Dockerfile" or <some name>.Dockerfile

buildtrigger/bitbuckethandler.py

@@ -1,23 +1,21 @@
 import logging
+import os
 import re
-
 from calendar import timegm
 
 import dateutil.parser
-
+from bitbucket import BitBucket
 from jsonschema import validate
+
+from app import app, get_app_url
+from buildtrigger.basehandler import BuildTriggerHandler
 from buildtrigger.triggerutil import (RepositoryReadException, TriggerActivationException,
                                       TriggerDeactivationException, TriggerStartException,
                                       InvalidPayloadException, TriggerProviderException,
                                       determine_build_ref, raise_if_skipped_build,
                                       find_matching_branches)
-
-from buildtrigger.basehandler import BuildTriggerHandler
-
-from app import app, get_app_url
-from bitbucket import BitBucket
-from util.security.ssh import generate_ssh_keypair
 from util.dict_wrappers import JSONPathDict, SafeDictSetter
+from util.security.ssh import generate_ssh_keypair
 
 logger = logging.getLogger(__name__)
 
@@ -455,10 +453,7 @@ class BitbucketBuildTrigger(BuildTriggerHandler):
       raise RepositoryReadException(err_msg)
 
     files = set([f['path'] for f in data['files']])
-    if 'Dockerfile' in files:
-      return ['']
-
-    return []
+    return ["/" + file_path for file_path in files if self.path_is_dockerfile(os.path.basename(file_path))]
 
   def load_dockerfile_contents(self):
     repository = self._get_repository_client()