http.Client: support InsecureSkipVerify

http.Client: support InsecureSkipVerify

This adds a new API http.NewNonSSValidating which ends up passing
InsecureSkipVerify: true all the way down the http stack. Because we
were using the global stdlib net/http.DefaultClient to enable
connection sharing, etc, we continue to cache the http.Client object.
I only create the object once we actually need it, and we only use it
for requests that also want to be "insecure".

I'm open to suggestions if we want to name the API differently. We
could also do it as a flag to New() but that is an API break (meaning
juju-core stops building until we patch juju-core). So I felt this was
a reasonable method.

This is step 2 in my work to support ssl-hostname-verify:false for the
Openstack provider. (bug #1202163)

https://code.launchpad.net/~jameinel/goose/httpclient-ssl/+merge/183844

Requires: https://code.launchpad.net/~jameinel/goose/httpsuite-ssl/+merge/183838

(do not edit description out of merge proposal)

[jameinel, 2013-09-04 10:44:34]

Please take a look.

[mue, 2013-09-04 10:51:12]

LGTM