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
(cherry picked from commit 6471776b6b25bb4062238f7c1b732b2d6999ec65)

Conflicts:

	nova/tests/virt/vmwareapi/test_vmwareapi_vim_util.py

Change-Id: I6b2e0ce664c0f6b479475a4bbc80947e5a1f9101
Merge "VMware: Fix unhandled session failure issues" into stable/havana