Show missing branches in coverage report.
Show missing branches in coverage report.

This used to be the default in coverage 3.x, but 4.0+ requires you to
explicitly configure it.

Change-Id: I3b06154c7862c300b5a2b3afb14cced1e8411468

openstack/swift,swiftstack/swift,matthewoliver/swift,matthewoliver/swift,smerritt/swift,tipabu/swift,tipabu/swift,openstack/swift,tipabu/swift,smerritt/swift,matthewoliver/swift,matthewoliver/swift,openstack/swift,openstack/swift,swiftstack/swift,tipabu/swift,swiftstack/swift,smerritt/swift,smerritt/swift