Prevent perfcounters from stopping MonitoringService

[niklasi]

On Windows you can get problems with corrupt peformance counters and
this can prevent the MonitoringService from saving stats.
Some calls to the perfcounters is wrapped in a try-catch with a retry,
but not all of them.

Fix: Handle the calls to the gc-stats perfcounters the same way as the
rest of the perfcounters.

[pgermishuys]

Looks good to me, waiting for the tests to pass.