set LANG=C prior to apt-get install

There are some problems during a remote ssh session attempting
to install maas wrt postgresql failing because of incorrect/
unknown locales.

LP: https://bugs.launchpad.net/maas/+bug/1382774

Fixes #236

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
1) the if will always pass because you're doing `if string or (needle in string)`
2) we should only bail if LC_ALL is set, LANG is not good enough