Adding start/stop functionality in manage.py (#457).  source.py and journalist.py create a pidfile (the path of which is defined in config/base.py) and this is referenced for shutdown.
Improving the start and stop process by getting return status from start-stop-daemon.
Removing restart from commands
Cleanup from rebase develop
allow reuse of _source_submits_a_file method in other functional tests
assert that a submitted secret message cannot be found in a memory dump of the source server
adds test case for message submission not being retained in memory
adds gdb dependency to vagrant, needed by new memory test
makes _source_submits_a_message function reusable
supressed gcore output in tests
make tests fail with the number of occurences of the secret_message in memory
Merge branch 'develop' into pr/458

Need to import config individually to get the PIDFILEs without messing up the
test config. Added comment to fix in the future.

Conflicts:
	securedrop/manage.py
Merge pull request #476 from jacksingleton/submission-in-mem-test

Test to check if the source submission is retained in memory