feat(build runner): added in context, dockerfile_location

this is a new feature meant to allow people to use any file as
  a dockerfile and any folder as a context directory

buildtrigger/basehandler.py

@@ -1,3 +1,4 @@
+import os
 from abc import ABCMeta, abstractmethod
 from jsonschema import validate
 from six import add_metaclass
@@ -290,7 +291,7 @@ class BuildTriggerHandler(object):
   def get_dockerfile_path(self):
     """ Returns the normalized path to the Dockerfile found in the subdirectory
         in the config. """
-    dockerfile_path = self.config.get('subdir') or 'Dockerfile'
+    dockerfile_path = self.config.get('dockerfile_path') or 'Dockerfile'
     if dockerfile_path[0] == '/':
       dockerfile_path = dockerfile_path[1:]
     return dockerfile_path
@@ -303,10 +304,11 @@ class BuildTriggerHandler(object):
     ref = metadata.get('ref', None)
     commit_sha = metadata['commit']
     default_branch = metadata.get('default_branch', None)
-
     prepared = PreparedBuild(self.trigger)
     prepared.name_from_sha(commit_sha)
-    prepared.subdirectory = config.get('subdir', None)
+    # TODO: Charlie Tuesday, March 28, 2017 come back and clean up subdirectory.
+    prepared.subdirectory = config.get('dockerfile_path', None)
+    prepared.context = config.get('context', None)
     prepared.is_manual = is_manual
     prepared.metadata = metadata
 
@@ -327,3 +329,28 @@ class BuildTriggerHandler(object):
     namespaces = list(namespaces_dict.values())
     validate(namespaces, NAMESPACES_SCHEMA)
     return namespaces
+
+  @classmethod
+  def get_parent_directory_mappings(cls, dockerfile_path, current_paths=None):
+    """ Returns a map of dockerfile_paths to it's possible contexts. """
+    if dockerfile_path == "":
+      return {}
+
+    if dockerfile_path[0] != os.path.sep:
+      dockerfile_path = os.path.sep + dockerfile_path
+
+    dockerfile_path = os.path.normpath(dockerfile_path)
+    all_paths = set()
+    path, _ = os.path.split(dockerfile_path)
+    if path == "":
+      path = os.path.sep
+
+    all_paths.add(path)
+    for i in range(1, len(path.split(os.path.sep))):
+      path, _ = os.path.split(path)
+      all_paths.add(path)
+
+    if current_paths:
+      return dict({dockerfile_path: list(all_paths)}, **current_paths)
+
+    return {dockerfile_path: list(all_paths)}