libvirt: Unnecessary instance.save(s) called

When spawning an instance there may a considerable amount of
instance.save() called. This is not necessary as the compute
manager will update the instance after the spawn method has
successfully completed.

Change-Id: I61610b3869caeb7822eab3f2d09335744b75db28
Closes-bug: #1366548
FIX: Fail to remove the logical volume

The logical volume can not be removed when delete VM error. I look at the
code, found that parameter is a list in the libvirt's lvm, but in
imagebackend, parameters passed is a string.

Change-Id: I222f6c5cfe5be63105f2fd8afd7ccd209ca2e5f7
Closes-Bug: #1358552
Revert "libvirt: reworks configdrive creation"

This reverts commit 228d0221763b12f11ecbacde4db38b1151f96e31.

This commit introduced bug 1369627 (a security vulnerability), as
well as misunderstanding how our image caching works for libvirt.
I think we can achieve the same thing in a much simpler manner.

Change-Id: I7ede9b0f77710869197d9b48c6dd6bbc3087738c
Merge "libvirt: Unnecessary instance.save(s) called"
Merge "FIX: Fail to remove the logical volume"
Merge "Revert "libvirt: reworks configdrive creation""