dogtag: Only call initialize() if crypto is not None
dogtag: Only call initialize() if crypto is not None

_setup_nss_db_services() can return None in case the config option
[dogtag_plugin]nss_db_path is not set.
In that case, don't call the initialize() method which would fail with:

AttributeError: 'NoneType' object has no attribute 'initialize'

Change-Id: Ia6ffc8945d8125047273872ba75f0b084dc5810f

openstack/barbican,openstack/barbican