df-server test mocking

df-server now supports end-to-end auth, so more advanced spring test setup is needed to support unit testing.

Do the following:
- mock the spring security context with username/password in the StoreImpl test suite.
- create a MockValve that implements IValve with very very basic behavior for unit testing
- remove any hardcoded URL's in df-server tests that rely on the Hashmapinc-hosted drilltest server.