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.
Can you add a description of this function as well? Also, we use ```:return:``` and ```:rtype:``` instead of the ```@``` style. Please also add ```:param:``` and ```:type:``` lines for the config.