Show an error message in the UI when scheduler returns an invalid response.

Show an error message when a call to the thrift end point returns an invalid response.

Testing Done:
gradle clean build.

Tested with local scheduler. Scheduler shows an error message (ex: when storage is not ready)

Bugs closed: AURORA-18

Reviewed at https://reviews.apache.org/r/17014/
Added docs about apache email setup.

Reviewed at https://reviews.apache.org/r/17068/