Fixes patch for JCLOUDS-155.

The problem reported in JCLOUDS-155 is that certain proxies lowercase
headers. This is especially a problem for the swift header
"X-Storage-Url", because it tells the client after authentication where
to go to next.
The patch originally put the value into a CaseInsensitiveMap, but it was
dropped not to add a dependency to apache commons.
When that was dropped the case insensitivity was still checked against,
but the map entries contained the original header name as key.

When then the factory tries to read AuthHeaders.STORAGE_URL from the map,
that value is not there.

This patch fixes also the test by testing that the new URL can be read
using that constant.