VMware: Fix unhandled session failure issues

VMware driver has a re-try mechanism to handle session expiration
failures. Due to a minor bug in the exception handling module, this
failure was unhandled.

The patch fixes this issue and has added tests.

Closes-Bug: #1252827
Change-Id: Ie91adb4b4b57b7cefeed855cdbe4710da86294f0
Clean up test cases for compute.manager._check_instance_build_time

This patch cleans up the unit tests related to the
_check_instance_build_time method so that they are actually verifying
the expected vm_state value when the instance is updated.

This patch also removes the test_instance_build_timeout test case
since it was completely redundant with the other one modified
here. I checked the git history and both test cases were added
in the same commit which confirms that they weren't added for
different reasons, i.e. separate bug fixes/use cases.

Change-Id: Ib384c84e2954bd303661386256053b3c1ad38239
Make flavor_access extension use Flavor object

This makes the flavor_access extensions use the Flavor object instead
of calling into the compute/flavors.py file entirely.

Related to blueprint compute-manager-objects

Change-Id: I360c28ad2a239b34822ba9dda3b5c583c8c886b3
Cells: check states on resize/rebuild updates

When the API cell receives instance updates, check the task states for
any resize and rebuild states.  Make sure to only apply them if the
current task state for the instance is what we expect.  This will fix
any out of order messages from potentially stomping on re-setting the
instance to ACTIVE/None on finish of the actions.

Change-Id: Id79e35e29170ac2b8f42a955cecaae3072aba09c
Closes-bug: 1249072
Merge "Clean up test cases for compute.manager._check_instance_build_time"
Merge "VMware: Fix unhandled session failure issues"
Merge "Make flavor_access extension use Flavor object"
Merge "Cells: check states on resize/rebuild updates"