Don't raise unnecessary stack traces in EC2 API

exception.EC2APIError exceptions are always expected, so no reason to have a
LOG.exception when one is raised.  Furthermore nova.api.ec2.ec2_error already
logs the exception so the duplicate log statement is just removed

Fix Bug 1180973

Change-Id: I4b42a9a764f6e15bb94a383e8a725d52d7436bd7
Use strict=True instead of `is_valid_boolstr`

Oslo's `bool_from_string` learned the `strict` keyword which allows
callers to detect invalid boolean values, so we can use that instead
of having a new Nova-specific function.

Change-Id: I61bfa4029897c7304bd54d6cdae9f9a9bc4c1f78
Remove unnecessary parens in test_volumes

Return statements were using unnecessary parens, this removes them.

Change-Id: Iee63ffa826d323a89493e16c1b9592bae74e350f
Merge "Don't raise unnecessary stack traces in EC2 API"