Description of problem:
Using exclamation character "!" on http_proxy password breaks connectivity

How reproducible:
Always

Steps to Reproduce:
1. hammer settings set --name http_proxy --value 'http://proxyuser:pass!@192.168.1.1:3128'

Actual results:
Executing "hammer subscription refresh-manifest --organization redhat" shows:
~~~
Manifest refresh failed:
407 "Proxy Authentication Required"
~~~

Expected results:
Manifest is refreshed