make test: don't run if other vpp process runs
make test: don't run if other vpp process runs

Check if there are existing vpp processes before running the test suite
and refuse to run if there are. This prevents the removal of other test
suite temporary files and also makes sure that if the machine is loaded
by (zombie) vpp processes, interactive tests (like bfd) won't fail.

Change-Id: I88a74098188cb3f51966de5db19d7f80f39e51e2
Signed-off-by: Klement Sekera <b8003f27414ca85c37624503b7b4e8f8c829bb4d@cisco.com>

FDio/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,milanlenco/vpp,vpp-dev/vpp,FDio/vpp,milanlenco/vpp,FDio/vpp,vpp-dev/vpp,FDio/vpp,milanlenco/vpp,vpp-dev/vpp,vpp-dev/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,chrisy/vpp,milanlenco/vpp,chrisy/vpp,milanlenco/vpp,chrisy/vpp,vpp-dev/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,milanlenco/vpp,FDio/vpp