Use ready_with_5_slaves tests testgroup when ready_with_7_slaves was used

we don't have snapshot ready_with_7_slaves in fuel-main yet
Added option to keep existing environment
Fixed qa_vcenter_test
Added datetime to name of the successful snapshot after tests end
Revert VMware snapshots after removing iptables rules

to avoid situations when env created faster then vmware
snapshots are reverted and thus affected by iptables rules
Unpause qa_vcenter vms after test succeeded
Updated qa_nsx script to match qa_vcenter
Ensure that previous environment with same name erased

if called without --existing key previous env with
same name should be erased, else there might be conflict
in network configuration
Added output of env name and net infos