Bug 1159067 - Read 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.
I suggest removing this comment for two reasons. 1) if the conf file ever moves then this is one more thing that needs to be updated. 2) the code is easy to ready so I don't think the comment provides any additional clarity.