Topology redeployment should be configurable

With a recent change for KNOX-2689, XML-based topologies are re-deployed only, if there is an actual change in the topology. This commit invalidates a well-known redeploy "technic" of touching the topology file.

lmccay indicated this in Knox's DEV/USER mailing lists so I discussed this matter offline with some Knox team members and we agreed the following should be implemented to make this behavior configurable and be backward compatible OOTB with previous Knox versions:

• a new gateway-site.xml param to be added, called gateway.topology.redeploy.requires.changes, to indicate if we equality check should be skipped. Defaults to false to be backward compatible.
• in DefaultTopologyService the redeploy logic I added recently should be modified to check if an equality check is needed or not