typo in maas-region-controller.postrm stops remove/purge from correctly calling dbconfig

line 9 of maas-region-controller.postrm tests for the existence of '/etc/dbconfig-common/maas.conf', which will not exist. the file that gets created is instead maas-region-controller.conf. since that test is never true, the call to dbc_go to do the postrm.pgsql stuff never happens.

This appears to contribute to some flakiness involving purging and reinstalling maas.

On one server that I'm currently having difficulty with, I had a /etc/dbconfig-common/maas-region-controller.conf that was two months (and several maas versions) old, despite having purged several times.

I think this is related to the error messages I was seeing when purging, including errors about wrong password for user maas. The local_settings.py I saw had a password of 'maas', but that .conf file had a different password.

Unfortunately, while this appears to be a legitimate typo bug, manually fixing it and re-running the purge did not fix my problems:

Setting up maas-region-controller (1.7.0~beta8+bzr3273-0ubuntu1~trusty1) ...
dpkg: error processing package maas-region-controller (--configure):
 subprocess installed post-installation script returned error exit status 10