Bug 1384518 - Vagrant: Simplify .profile helper functions
Bug 1384518 - Vagrant: Simplify .profile helper functions

Uses our custom `clear_cache` Django management command instead of
restarting memcached, since (a) for memcached has the same effect,
(b) will continue to work even after we switch to Redis (which instead
persists cache contents across server restarts).

Removes the `threstartmemcached` command since IMO it's no simpler
than just running `./manage.py clear_cache` on its own.

edmorley/treeherder,edmorley/treeherder,KWierso/treeherder,KWierso/treeherder,KWierso/treeherder,edmorley/treeherder,edmorley/treeherder,KWierso/treeherder