Add clone and single vm concurrent tests (#802)
Add clone and single vm concurrent tests (#802)

* Move concurrent tests to its own test case
Add getClients() for client init/connect
Change parallel* constants to flags @msterin

* Add concurrent cloning test

* Add concurrent test for the same docker host

* Use fmt for string formatting

@msterin

* Adjust clone size

pshahzeb/vsphere-storage-for-docker,luomiao/docker-volume-vsphere,govint/docker-volume-vsphere,luomiao/docker-volume-vsphere,shuklanirdesh82/docker-volume-vsphere,venilnoronha/docker-volume-vsphere,shivanshu21/docker-volume-vsphere,govint/docker-volume-vsphere,luomiao/docker-volume-vsphere,govint/docker-volume-vsphere,lipingxue/docker-volume-vsphere,pshahzeb/vsphere-storage-for-docker,lipingxue/docker-volume-vsphere,shuklanirdesh82/docker-volume-vsphere,shuklanirdesh82/docker-volume-vsphere,venilnoronha/docker-volume-vsphere,pshahzeb/vsphere-storage-for-docker,pshahzeb/vsphere-storage-for-docker,brunotm/docker-volume-vsphere,shuklanirdesh82/docker-volume-vsphere,ashahi1/docker-volume-vsphere,luomiao/docker-volume-vsphere,pshahzeb/vsphere-storage-for-docker,lipingxue/docker-volume-vsphere,brunotm/docker-volume-vsphere,shivanshu21/docker-volume-vsphere,venilnoronha/docker-volume-vsphere,venilnoronha/docker-volume-vsphere,luomiao/docker-volume-vsphere,luomiao/docker-volume-vsphere,brunotm/docker-volume-vsphere,venilnoronha/docker-volume-vsphere,brunotm/docker-volume-vsphere,shivanshu21/docker-volume-vsphere,shuklanirdesh82/docker-volume-vsphere,ashahi1/docker-volume-vsphere,lipingxue/docker-volume-vsphere,ashahi1/docker-volume-vsphere,shuklanirdesh82/docker-volume-vsphere,shivanshu21/docker-volume-vsphere,govint/docker-volume-vsphere,ashahi1/docker-volume-vsphere,ashahi1/docker-volume-vsphere,pshahzeb/vsphere-storage-for-docker,shivanshu21/docker-volume-vsphere,govint/docker-volume-vsphere,shivanshu21/docker-volume-vsphere,brunotm/docker-volume-vsphere,lipingxue/docker-volume-vsphere,brunotm/docker-volume-vsphere,govint/docker-volume-vsphere,lipingxue/docker-volume-vsphere,venilnoronha/docker-volume-vsphere,ashahi1/docker-volume-vsphere