Change in FreeBSD user add() home parameter handling.

Previously the module used -b to create a home directory that caused
some bugs. Change the module to use -d argument. This will fix the
issues when salt user defines a unusual home parameter and will also
fulfill the requirement that home directory's base directory should not
be created automatically.
Remove unused 'import os' from pw_user
Merge pull request #11791 from toddnni/develop

Change in FreeBSD user add() home parameter handling.