Modify the way we detect SELinux to use selinuxenabled instead of using
a try/except.
Handle SASL/GSSAPI authentication failures when getting a connection
Create separate object for Users and Groups (using same base class)
Check for uniqueness before adding new users and groups
Remove user_container from everything but add operations
Abstract out a number of functions that are common across users and groups
Make sure all strings passed in to be in a filter are checked
Add new error message: No modifications specified
