Set KVM usage false by defualt

As temporary fix to get instances Active,
we need use qemu in sys tests
Change KVM_USE value in setting.py by default
false value, if os environ is not defined
Add else part in fuel_web client to
verify if KVMS_USE false, update OS setting to qemu

Change-Id: Ifc817104d6b8a6d3a5de27c10c07afcdc92f283f