EUCA-5899 Created a cache for disk operations in EC2 to total all values from ephemeral values, also allowing "0" values if no ephemeral volumes exist (like BFEBS)

commit 7c9a7d7723a6d6829e829ddf3a56e5a846e10376
Merge: 8e7c799 2b6e695
Author: Evan Thomas <ethomas@eucalyptus.com>
Date:   Wed May 8 09:56:39 2013 -0700

    Merge branch 'dev/dmitrii/EUCA-5899' into dev/ethomas/EUCA-5899

commit 2b6e69542194923c6090e8e363cd16bc7af06446
Author: Dmitrii Zagorodnov <dmitrii@eucalyptus.com>
Date:   Fri Apr 26 16:27:00 2013 -0700

    Switching from 'root' to 'vol-...' dimension on NC

    Partially fixes EUCA-5899