move loading of config files to vsphere_helper
close the vsphere connection when we're done with it
shutdown vms after acceptance test run unless --preserve-hosts is passed
retry vsphere connection if failure 5 times
cleanup vsphere_helper
resume blimpy working correctly since multi hypervisor support

make vsphere cleanup work with multi-hypervisors

disable vsphere until Enterprise jobs are cleaned up
Do not retry failed vSphere connections
use Class methods for Class method dependencies
Documentation update
Merge pull request #340 from justinstoller/maint/master/improve_vsphere_performance

(maint) improve vsphere performance