Distinguish over-quota for volume size and number.
Distinguish over-quota for volume size and number.

Fixes LP 1020634

Ensure that exceeding the allowed number of volumes is not
mis-represented in log messages and exception handling as
excessive space usage.

Change-Id: I71ec995c77bc447bfc9221084b057bd8d69a4513

openstack/oslo.versionedobjects,citrix-openstack-build/oslo.versionedobjects