Clean up openstack-common.conf

The issues are detected by new change about update.py
in I68c0108304be8a315bcefe939c22019caab9bc98. This patch
doesn't depend the oslo-incubator patch.
 * Remove unused module crypto, sslutils, systemd, context,
   eventlet_backdoor
 * Add missing module wsgi, network_utils in openstack-common.conf

Change-Id: Ifeee85643e1242fc74eefc109719a02470888200
Merge "Clean up openstack-common.conf"