Add service broker to document_api
endpoint for updating service brokers

[#54734838]
pulled admin check into one place
Merge pull request #72 from drnic/docapi_broker

Add service broker to document_api
Simplify uniqueness validation tests

Using the existing test data to create the duplicate records means not
needing to rebuild the request body.
Check service broker API on creation

Verifies that v3 endpoint is reachable and responds appropriately.

[#54226274]
Small refactor in ServiceBrokersController

[#54734838]
add Task object

sends task.start on create and task.stop on delete
Raise duplicate instance exception for AppDirect ErrorResponse

The AppDirect gateway has been modified to return JSON encoded
exceptions. This requires a change to the exception handling code
related to service instance creation.
store Task secure token in database (encrypted)
Bump vcap_common
Handle more possible service broker check failures

The broker may not be reachable because (1) its host could not be
resolved, (2) the connection attempt timed out, or (3) the server
refused our connection.
Service Broker API ignores unmodifiable fields

 - For update and create endpoints.
[#55043026]
added configurable feature flag for tasks endpoint
Added spec for cloud controller config.
Merge pull request #76 from geapi/refactor_for_custom_buildpacks

Added spec for cloud controller config.

@aramprice / @jfoley
Add documentation_url to services

[#51374249]
Bump vcap_common
Ignore HM start requests if droplet_sha not yet known

This way, the crash logs for a newly deployed, crashed app can be viewed
immediately after cf push.

[#55409154]