* swarm/pss: fixed bug in pss.process, test added

* swarm/pss: test case updated

* swarm/pss: WaitTillSnapshotRecreated() func added

* swarm/pss: snapshot test updated

* swarm/pss: WaitTillSnapshotLoaded() fixed

* swarm/pss: gofmt applied

* swarm/pss: refactoring, file renamed

* swarm/pss: input data fixed

* swarm/pss: race condition fixed

* swarm/pss: test timeout increased

* swarm/pss: eliminated the global variables

* swarm/pss: tests added

* swarm/pss: comments added

* swarm/pss: comment fixed

* swarm/pss: refactored according to review

* swarm/pss: style fix

* swarm/pss: increased timeout