Bug 1159067 - [RFE] user cred from config

Bug 1159067 - [RFE] allow pulp to read user credentials from users admin.conf
if he/she does not want to provide password on command prompt
or --password in pulp-admin

this is basically for writing a batch job that would include multiple command lines together.
What can raise NameError? It looks to me like the _get_*_from_config functions are pretty guarded. If nothing can raise NameError, it would be cleaner to eliminate this try/except block.