Migration to oslo.utils

Common code from sahara.openstack.common.db was replaced
by usage of oslo.utils library.
sahara/openstack/common/network_utils.py module was removed.
excutils.py, importutils.py, timeutils.py and importutils.py
modules are waiting for migration to oslo.utils in other
oslo-incubator modules and still exist.

Change-Id: I6a82a9dfdf704da16ed709c650fa68f9527fd668
Merge "Migration to oslo.utils"