Add helper method in FairSchedulerAppsBlock to print app info

The various *AppsBlock classes are riddled with statements like:

.append(appInfo.getReservedVCores() == -1 ? "N/A" : String.valueOf(appInfo.getReservedVCores()))

The code would be much cleaner if there were a utility method for that operation, e.g.:

.append(printData(appInfo.getReservedCores()))