tests/migration-test: Silence the kvm_hv message by default

tests/migration-test: Silence the kvm_hv message by default

When running "make check" on a non-POWER host, the output is quite
distorted like this:

  [...]
  GTESTER check-qtest-nios2
  GTESTER check-qtest-or1k
  GTESTER check-qtest-ppc64
Skipping test: kvm_hv not available Skipping test: kvm_hv not available Skipping test: kvm_hv not available Skipping test: kvm_hv not available   GTESTER check-qtest-ppcemb
  GTESTER check-qtest-ppc
  GTESTER check-qtest-riscv32
  GTESTER check-qtest-riscv64
  [...]

Move the check to the beginning of the main function instead, so that
we do not have to test the condition again and again for each test,
and better use g_test_message() instead of g_print() here, like it is
also done in ufd_version_check() already.

Reviewed-by: Markus Armbruster <[email protected]>
Signed-off-by: Thomas Huth <[email protected]>
Message-Id: <1534419358[email protected]>
Reviewed-by: Juan Quintela <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>