Adds instance lock check for live migrate

Whilst migrate has an instance locked check, live migrate didn't. This patch
adds a check to see if the instance is locked in the compute api live migrate.

Adds a testcase for V3 and generic instance lock checking for the V2 API since
none existed yet.

Closes-bug: 1257187

Change-Id: I442abb74fe2a4d5d46b597b0ea24d249d2d03b45
Merge "Adds instance lock check for live migrate"