Downgrade target create failure mesg to warning

Since this will occur more often than we would like and
almost always recovers, change the log level to warning
instead of error.

This is to comply with the desire of the QA team to eradicate
error messages from succesful tempest runs.

Change-Id: If1a841bbeb9a36ff7e103a0e9aff67fda66a7f3b
Closes-Bug: #1243840
Handle NotFound exceptions in API

There were a number of calls in the API that
weren't catching NotFound exceptions.  The result is
unhandled exception traces and errors in the logs on good
runs in tempest.

Basicly any negative test that requests a non-existent element
would result in an unhandled exception.  This patch adds try/except
around the volume_api.getxxx calls in cinder/api/... methods to
clean this up.

Closes-bug: #1243485

Change-Id: I902acc7f4fdbc20fdb1a68697679417694c5533e
Merge "Handle NotFound exceptions in API"
Merge "Downgrade target create failure mesg to warning"