Make configure-qpid.sh non-destructive.

 * Sign with certutil instead of openssl

   Using certutil let's us sign with whatever CA is in the Qpid NSS DB,
   instead of having to have the CA cert and key out somewhere in the file
   system.  This situation is mainly of concern when running the script
   where a Qpid CA is already in the NSS DB.

 * Handle duplicates in the NSS DB.
 * Use existing Katello Candlepin certs.
 * Use cert fingerprints for comparison.
 * Use Katello cert alias when appropriate.
Compare the keys in the Tomcat keystore with the Candlepin keystore.

Generally speaking the Tomcat keystore should be a symlink to the
Candlepin keystore, but if it isn't and the keystores are out of sync
users will get strange and cryptic SSL errors.
Quote all paths.
Play nicely with a CA in an /etc/qpid/brokerdb NSS db.

Also use sudo for every certutil command because the command will fail
due to permissions if reading /etc/qpid/brokerdb.
Merge pull request #723 from candlepin/awood/qpid-idempotent

Make configure-qpid.sh non-destructive.