This fix will make sure that the nova-secret file will
be created with save "0600" (r--) permissions.
Additionally a new task will make sure that the file is removed
from the filesystem. This will minimize any unprivileged exposure
to the nova-secret file content.
Change-Id: I1c3ec322b2a661cf7dce0334866c90201bbef0a0
Closes-Bug: #1519088
eca0f5ddfb