Clear remote fs backend env cache on master start (2014.1 branch)

Clear remote fileserver backend env cache so it gets recreated during
the initial loop_interval. Allows envs to be rebuilt if changes are made
to an env whitelist/blacklist.

**Note: the whitelist/blacklist feature is not going to be in any of the Hydrogen releases, however this issue could still impact users in cases where a remote is deleted and there are no other immediate changes to any of the remotes that would result in the fileserver cache being updated (and thus the re-creation of the env cache). An edge case, but one worth fixing for 2014.1.1.**