added heartbeat for DB; changed heartBeatResponse message so it is the same as Special:HealthCheck message
Fixed formatting
used HTTP headers to send proper information to Nagios; displays "OK" message for Varnish always except when all database node are down
js-beautified
refactoring
CR changes: cached headers values, moved hardcoded values to variables
CR changes: passed error code as a 2nd parameter of getDbNodeHeartbeat()
fixed exit code for slave down
js-beautified
removed unnecessary variables, changed dictionary and getDbHeartbeat() method
added new entry point for nagios
CR change: addressed code review note about renaming a method
Merge pull request #179 from Wikia/MOB-1891

Tested, EiA