qemu.tests.hypervisor_flag: test for 'hypervisor' flag

Sanity check for 'hypervisor' flag in cpuinfo for the running guest VM.

    1) Get a living VM
    2) Establish a remote session to it
    3) Grab information from /proc/cpuinfo
    4) Test if it has 'hypervisor' flag

Signed-off-by: Ruda Moura <rmoura@redhat.com>