Updating the try/except blocks to assertRaises.

Tests Modified:
test_get_metadata_of_alt_account_image_fails
test_delete_metadata_of_alt_account_server_fails
test_delete_metadata_of_alt_account_image_fails

Modifications:
As per new Tempest style guidelines, convert "try/expect/else"
statements into "assertRaises".

In order to ensure that other tests remain unaffected
because of this change, replace "finally" with "addCleanup".

Parially implements Blueprint update-expected-exception-tests.

Change-Id: Iac2a911ee6f812e18f41e66ac6d7fd648ce2f1fa
Remove skips in volume types tests.

This commit removes the skips from test_volume_types_extra_specs_negative
for bugs that have been marked as fixed. However, the XML client class was
not written to accept the bad input for the negative tests. So the XML
client is modified to accept this input. Additionally, the skip in
test_volume_types_negative.py was removed as well.

Change-Id: I45090c29a4115c205b656777e57a940a7de7dbf5
Merge "Updating the try/except blocks to assertRaises."