Don't return from a finally block

The code in the finally block always executes, even if an exception is
raised. If a return is done, that will cause exceptions to be silently
ignored.

Some unit tests have been failing because of API changes to the
nova.compute.manager:ComputeManager._delete_instance method but the
use of finally/return ended up silently ignoring that error and
caused the test to appear as if it was passing. Another unit test
fails because of a missing uuid attribute.

It could also potentially cause other exceptions to be ignored at
runtime (such as SystemExit) which is likely not the intended
behavior.

Change-Id: I083ee7215296e35a0027be5b3ddf8b764f44cc5b
Closes-bug: 1324277
Merge "Don't return from a finally block"