[1094540] Agents get permanently backfilled if backend database goes offline for a moment
Clean up some of the live availability doco/workflow:
- Fix the jdoc for DiscoveryAgentService.getCurrentAvailability() to reflect reality
- Fix ResourceManagerBean.getLiveResourceAvailability() to mark its avail report
  as a "ServerSideReport".  This prevents it from interfering with server-agent
  backfill coordination.  Also, correct some confusing inline doco and doe some cleanup.
- Fix AvailabilityManagerBean.mergeAvailabilityReport() such that logic checking for the
  backfill flag does not execute *after* the backfill flag has been reset. And clean up
  the overall logic a bit more.
- Improve jdoc for AvailabilityManagerLocal.updateLastAvailabilityReportInNewTransaction
  to clearly indicate its side-effect of clearing the backfill flag.

Conflicts:
	modules/core/client-api/src/main/java/org/rhq/core/clientapi/agent/discovery/DiscoveryAgentService.java
	modules/enterprise/server/jar/src/main/java/org/rhq/enterprise/server/resource/ResourceManagerBean.java

Cherry-Pick master 2fa7c545cb0225916ae27965a143de2a6f85748f