Revert "CA-114341: check return value of LVHD plugins"

This reverts commit 4bdb01aa761d73519c2e14410a3e63f291918524. We revert
the commit because it uncovers an existing bug (fixing it is not
trivial) and makes the BVT and BST fail, blocking the merge of
trunk-storage into trunk.

Signed-off-by: Thanos Makatos <thanos.makatos@citrix.com>
Reviewed-by: Vineeth Thampi Raveendran <vineeth.thampi@citrix.com>

GitHub: closes #100 on xapi-project/sm
CA-126097: Handle vm-clone when VBD is attached.

A clone operation was never performed when the VM is running, as a result
there is no need to pause/unpause tapdisk during the clone operation. With
vm-copy in place, there is a change in this behaviour. vm-copy attaches
and activates the VBD, a clone operation during the phase could result
in VHDs in inconsistent state.

Signed-off-by: Vineeth Thampi Raveendran <vineeth.thampi@citrix.com>
CA-126097: Addressing review comments