vm-report: Do not report back unless systemd says we're up

There are instances when this script may begin execution before systemd
says that all services have been started and the system is "booted".
Until that time systemd-analyze will not report its timestamps as they
have not completed.
This ensures all tested guest VMs report back once they have been declared
fully booted - ensuring results are not skewed by udev rules, etc.

Signed-off-by: Ikey Doherty <michael.i.doherty@intel.com>