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.
maybe replace this with a sentence like: "The following snippet is from ``~/.pulp/admin.conf``. That way if the length of admin.conf changes it will still be right.