Use testr to run nova unittests.
Use testr to run nova unittests.

Convert nova from using nosetests to testr for its test runner. Some
tests had to be modified to get them to run properly under testr.

run_tests.sh has been updated to run testr instead of nosetests.

Coverage is collected by running subunit.run under coverage.py when the
coverage environment is selected.

Note that you will need to rebuild your virtualenvs as nose is being
removed from the dependency lists and is being replaced by testr. Tests
will run in different processes once this test is merged so you cannot
use test classes to pass information between tests. Each test should be
a proper independent unit. Additionally the -x and -d flags to
run_tests.sh have been removed as there are currently no decent
approximations for those functions.

Change-Id: I019ca098972ca749b195f59968cf21edd5ba9109

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