Support LDAP users

[MrPointer]

Motivation

Some machines, mainly at work, have the user configured as an LDAP user rather than a local one.
LDAP users require a different approach since their uid/pid is auto-generated (IDC how...), and they aren't managed in /etc/passwd.
There are probably more differences left to explore, so it will require lots of testing.

Implementation

Changing the default shell

Ubuntu provides a utility to change the default shell for an LDAP user, does so by updating the LDAP server with this info.