Add a test program for testing the CRB with the external swtpm.

The 1st test case extends a PCR and reads back the value and compares
it against an expected return packet.

The 2nd test case repeats the 1st test case and then migrates the
external swtpm's state along with the VM state to a destination
QEMU and swtpm and checks that the PCR has the expected value now.

The test cases require 'swtpm' to be installed on the system and
in the PATH and 'swtpm' must support the --tpm2 option. If this is
not the case, the test will be skipped.
Signed-off-by: NStefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: NMarc-André Lureau <marcandre.lureau@redhat.com>