libvirt: convert test_dmcrypt to avoid DB usage

Nothing in the dmcrypt test case uses the DB, so it was
incurring the DB setup penalty for no gain. Switch to
use NoDBTestCase reducing time from 1.7s to 0.09s

Partial-bug: #1369516
Change-Id: Ifd4b919f60f48f691d83cedb6ce7ea18c98636ad
libvirt: convert encrypted LVM test to avoid DB usage

The EncryptedLvmTestCase test case was depending on the DB setup
for no purpose. This masked a bug whereby the test was relying
on the implicit import of nova.keymgr.conf_key_mgr config opts.
Explicitly import the config opt and remove DB setup. This
improves performance from 1.8s to 0.6s

Partial-bug: #1369516
Change-Id: Icd5c27b3ac6cab5a014fae65904bbbefb5343282
Merge "libvirt: convert test_dmcrypt to avoid DB usage"
Merge "libvirt: convert encrypted LVM test to avoid DB usage"