neutron-base: remove bashisms
neutron-base: remove bashisms

Use [ instead of [[.

This will solve the following issue:

Change-Id: I1153a5146ca8b08dd1ad732b60d8d4bce8e060ab
INFO:kolla.common.utils.neutron-base:/bin/sh: 1: [[: not found
INFO:kolla.common.utils.neutron-base:/bin/sh: 1: [[: not found
INFO:kolla.common.utils.neutron-base:/bin/sh: 1: [[: not found
INFO:kolla.common.utils.neutron-base:/bin/sh: 1: [[: not found
INFO:kolla.common.utils.neutron-base:/bin/sh: 1: [[: not found
INFO:kolla.common.utils.neutron-base:/bin/sh: 1: [[: not found
INFO:kolla.common.utils.neutron-base:

rahulunair/kolla,openstack/kolla,openstack/kolla,rahulunair/kolla,stackforge/kolla,stackforge/kolla,stackforge/kolla