Dell: Added verify cert option for REST calls

Dell: Added verify cert option for REST calls

If one goes through the trouble to create a cert and
install it on the Dell Data Collector and on the cinder
node then we can enable certificate verification on the
request calls to the Dell REST API.

This simply makes dell_sc_verify_cert a cinder.conf option
for a Dell backend and directly uses that as the verify
option on the REST requests.  Default is False.

The update_migrated_volume function arrived via a rebase
and had a merge issue that was fixed.  Specifically the
dell_sc_ssn value is no longer part of the api.find_sc
call.

Spelling error also corrected in a LOG message.

SecImpact

Change-Id: I22348d5e0b55d56f44f1fc4f0c830790a6670494
Implements: blueprint dell-sc-add-verify-cert