SSH key disassociation fix
Fix ability to delete key association with old backend.

Don't check if backend_id in user.backends when disassociating keys,
so that old associatiations with machines in removed backends can
be deleted.
Fix issue with last key not disassociating properly in some cases
Fix issue with bash script that removes keys from authorized_keys

The command sent over ssh when associating keys looked like:
grep -v "$pub_key" ~/.ssh/authorized_keys > ~/.ssh/authorized_keys.tmp &&
mv ~/.ssh/authorized_keys.tmp ~/.ssh/authorized_keys

However, when dissasociating the last key, grep -v returns empty string.
That is seen as an error status so '&& mv' never gets executed.

That means we were never actually able to disassosiacate the last
remaining SSH key from authorized keys.

Changed '&&' to ';' so that mv is always executed.
Fix issue with missing new line in end of authorized_keys

Change key deployment bash script to gracefully handle the
case where there is no new line in the end of authorized_keys.
Merge pull request #38 from mistio/disassoc_key_fix

Disassoc key fix