respect http(s)_proxy env variable for proxy information

The idea behind this is to allow a user to specify the username/password
and other proxy information in an environment variable instead of
the configuration file. Subscription manager will use the values passed in from
the cli or from the configuration file if present otherwise it will try to use
the http(s)_proxy environment variables. The variables are read in the following
order:

HTTPS_PROXY
https_proxy
HTTP_PROXY
http_proxy

Summary of changes:

    * moved parse_url, ServerUrlParse* exceptions, has_(good|bad)_scheme
      to python-rhsm
    * cp_provider, managergui, managercli, repolib use the new
      utility method from python-rhsm.
    * updated rhsm_login to use the new utils package from python-rhsm
    * migrate were untouched.

use rhsm.utils
bump python-rhsm requires
add comment
move the proxy information to python-rhsm
Merge branch 'master' into newproxypass
Merge branch 'master' into newproxypass

Pull requests.
add ServerUrlParseException strings to mapper

When we moved the utils code from subscription-manager to
python-rhsm, we had a bunch of nice exceptions with translations.
These translations lived in subscription-manager. So to keep
them there, we used the new exception mapper feature. This means
they go away from python-rhsm and just generic exceptions.
remove proxy env from repolib.

Per review, we wanted to remove it from repolib, this assumes yum does the
right thing with the proxy info.
do not pass proxy information to ContentConnection.

We were passing the proxy information from the configuration file
to ContentConnection which is no longer necessary based on the
recent changes to python-rhsm where we look at the values passed
in, configuration file OR environment variable.
don't use env proxy for network config.
Merge pull request #835 from candlepin/newproxypass

respect http(s)_proxy env variable for proxy information