Bug 1159067 - [Work in Progress] 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.
sure, I will add the param and type docstrings.
The remainder of the code uses @style. If I use :style, the code would have inconsistent doc strings.