Pass certificate, key and cacert to glanceclient

When glance is configured with ssl nova does not pass it's certificate,
key, or cacert.  Updated the code to pass the certificate, key, and cacert used in the
nova.conf file, if they are set.  Removed nested if statement.

Change-Id: I23fcd070994e435cb42aa09c824d13553503a7c5
Closes-Bug: #1279381
Merge "Pass certificate, key and cacert to glanceclient"