travis: allow to run up to two tests in parallel
travis: allow to run up to two tests in parallel

It works faster and checks that two criu processes can work concurrently.

Signed-off-by: Andrei Vagin <74c05afa918858348d6db8037d82fa8124870113@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@virtuozzo.com>

KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote,KKoukiou/criu-remote