Several issues in vmware collector main loop

When a vmware service performance counters are updated it calculates nearest vmware service update time incorrectly. If the configured cache update frequency is less than the real update time, other vmware collectors try to lock the service for update without sleeping.

Depending on configuration this may result in more cpu usage and vmware locking, but, unless DebugLevel 4 is specified, it should not affect disk utilization mentioned in ZBX-9466.