SCVMM scheduled EMS refresh.

A mechanism was needed to refresh the SCVMM provider given that event support will not be in the 3.1 release. I have configured a 4 minute schedule but am open to negotiation on the frequency. On one hand we need to bear in mind that an EMS refresh can take more than 4 minutes but on the other hand we can't wait too long after a VM power operation.
Merge pull request #308 from bronaghs/scvmm_refresh_schedule

SCVMM scheduled EMS refresh.