I ran into the problem mentioned (on install) and I also ran into the same problem when trying to remove maas packages:

ubuntu@maas:~$ sudo apt-get autoremove maas maas-dhcp maas-dns
[sudo] password for ubuntu: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  maas maas-cluster-controller maas-dhcp maas-dns
0 upgraded, 0 newly installed, 4 to remove and 0 not upgraded.
2 not fully installed or removed.
After this operation, 352 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 50526 files and directories currently installed.)
Removing maas (1.5.1+bzr2269-0ubuntu0.1) ...
Removing maas-cluster-controller (1.5.1+bzr2269-0ubuntu0.1) ...
maas-cluster-celery stop/waiting
maas-pserv stop/waiting
Removing maas-dhcp (1.5.1+bzr2269-0ubuntu0.1) ...
Removing maas-dns (1.5.1+bzr2269-0ubuntu0.1) ...
 * Stopping domain name service... bind9                                        waiting for pid 661 to die
                                                                         [ OK ]
 * Starting domain name service... bind9                                 [ OK ] 
Processing triggers for man-db (2.6.7.1-1) ...
Setting up maas-region-controller (1.5.1+bzr2269-0ubuntu0.1) ...
 * Stopping web server apache2                                                   * 
 * Restarting PostgreSQL 9.3 database server                             [ OK ] 
Considering dependency proxy for proxy_http:
Module proxy already enabled
Module proxy_http already enabled
Module expires already enabled
Module wsgi already enabled
 * Restarting message broker rabbitmq-server                             [ OK ] 
Changing password for user "maas_longpoll" ...
...done.
Changing password for user "maas_workers" ...
...done.
Syncing...
Traceback (most recent call last):
  File "/usr/bin/django-admin", line 5, in <module>
    management.execute_from_command_line()
  File "/usr/lib/python2.7/dist-packages/django/core/management/__init__.py", line 399, in execute_from_command_line
    utility.execute()
  File "/usr/lib/python2.7/dist-packages/django/core/management/__init__.py", line 392, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/lib/python2.7/dist-packages/django/core/management/base.py", line 242, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/usr/lib/python2.7/dist-packages/django/core/management/base.py", line 285, in execute
    output = self.handle(*args, **options)
  File "/usr/lib/python2.7/dist-packages/django/core/management/base.py", line 415, in handle
    return self.handle_noargs(**options)
  File "/usr/lib/python2.7/dist-packages/south/management/commands/syncdb.py", line 90, in handle_noargs
    syncdb.Command().execute(**options)
  File "/usr/lib/python2.7/dist-packages/django/core/management/base.py", line 285, in execute
    output = self.handle(*args, **options)
  File "/usr/lib/python2.7/dist-packages/django/core/management/base.py", line 415, in handle
    return self.handle_noargs(**options)
  File "/usr/lib/python2.7/dist-packages/django/core/management/commands/syncdb.py", line 57, in handle_noargs
    cursor = connection.cursor()
  File "/usr/lib/python2.7/dist-packages/django/db/backends/__init__.py", line 159, in cursor
    cursor = util.CursorWrapper(self._cursor(), self)
  File "/usr/lib/python2.7/dist-packages/django/db/backends/__init__.py", line 129, in _cursor
    self.ensure_connection()
  File "/usr/lib/python2.7/dist-packages/django/db/backends/__init__.py", line 124, in ensure_connection
    self.connect()
  File "/usr/lib/python2.7/dist-packages/django/db/utils.py", line 99, in __exit__
    six.reraise(dj_exc_type, dj_exc_value, traceback)
  File "/usr/lib/python2.7/dist-packages/django/db/backends/__init__.py", line 124, in ensure_connection
    self.connect()
  File "/usr/lib/python2.7/dist-packages/django/db/backends/__init__.py", line 112, in connect
    self.connection = self.get_new_connection(conn_params)
  File "/usr/lib/python2.7/dist-packages/django/db/backends/postgresql_psycopg2/base.py", line 116, in get_new_connection
    return Database.connect(**conn_params)
  File "/usr/lib/python2.7/dist-packages/psycopg2/__init__.py", line 179, in connect
    connection_factory=connection_factory, async=async)
django.db.utils.OperationalError: FATAL:  password authentication failed for user "maas"
FATAL:  password authentication failed for user "maas"


This is just extra information and is most likely a result of the first re-install failure.