vmware: intermittent failure in test_vmware_vmdk

There was a race condition between the two Event() objects being
created within loopingcall and Retry in api module. Did away with
the Event object in Retry and used loopingcall the right way.

Change-Id: I2534bad9294747fcd618ba3634abb01ceef92213
Merge "vmware: intermittent failure in test_vmware_vmdk"