Fixed JUnit tests.

Conflicts:

	src/main/java/net/floodlightcontroller/util/TimedCache.java

After a switch is asynchronously removed due to another switch with the
same DPID connecting, the first switch might still have messages qeued.
If we process these messages after removing the switch switch listeners
can get confused.

[#23382219]

When a switch with an already existing DPID connects, close the
connection from the previously connected switch.

[#23382219]

Move the switchcluster REST API from /wm/core/controller/switchclusters/json to /wm/topology/switchclusters/json. [#23518013]

2 - Added more comments to TopologyImpl.

First checking for ITopology REST API. Links between OpenFlow switches connected to the controller can now be seen through /wm/topology/links. [#23518013]

2 - Added a call to change StaticFlowPusher push interval
3 - Added various comments

2 - Added a call to change StaticFlowPusher push interval
3 - Added various comments

Conflicts:

	src/main/java/net/floodlightcontroller/topology/internal/TopologyImpl.java

Clean-up of and javadoc to switch cluster computation code and corresponding
data structure.

Rewriting switch cluster computation to return strongly connected components in the presence of unidirectional links.  The notion of internal switchPort is also changed.