Bug 1115527

+++ This bug was initially created as a clone of Bug #1115516 +++

Description of problem:
A RHEL-7 system registered to Red Hat Satellite won't be able
to communicate with it parent over a Squid proxy.

Version-Release number of selected component (if applicable):
yum-rhn-plugin-2.0.1-4.el7

How reproducible:
Always

Steps to Reproduce:
1. RHEL-7 system, registered to Red Hat satellite 5.6 (or later)
2. Configure /etc/sysconfig/rhn/up2date to use a squid proxy
   (enableProxy, httpProxy options)
3. Configure iptables so that the parent is not directly accessible,
   only the Squid proxy is.
3. yum clean all && yum makecache

Actual results:
# yum clean all
Loaded plugins: langpacks, rhnplugin
Cleaning repos: test-channel-01
Cleaning up everything

# yum makecache
Loaded plugins: langpacks, rhnplugin
This system is receiving updates from RHN Classic or Red Hat Satellite.

The process freezes here ^^

lsof reveals, that yum is trying to connect to the parent Satellite, rather
than the configured Squid proxy.

# lsof -p 9213|grep TCP
yum     9213 root   11u  IPv4              90353       0t0      TCP xen86.englab.brq.redhat.com:37308->xen58.englab.brq.redhat.com:https (SYN_SENT)

Expected results:
yum operations over proxy works.

Additional info:
XML-RPC requests (for example when yum-rhn-plugin wants to get the list of channels)
works correctly. The problem is when we're setting up URLGrabber objects
for proxy communication (i.e. the actual metadata and package retrieval
operations won't work).