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>
spew will overwrite the file? I think this should just be an append.