test, seccomp, Makefile: Switch to valgrind runs for passt functional tests

Pass to seccomp.sh a list of additional syscalls valgrind needs as
EXTRA_SYSCALLS in a new 'valgrind' make target, and add corresponding
support in seccomp.sh itself.

In test setup functions, start passt with valgrind, but not for
performance tests.

Add tests checking that valgrind exits without errors after all the
other tests in the group are done.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

test/run

@@ -78,14 +78,23 @@ run() {
 	test dhcp
 	test tcp
 	test udp
+	test valgrind
 	teardown passt
 
+	VALGRIND=1
 	setup passt_in_ns
 	test ndp
 	test dhcp
 	test icmp
 	test tcp
 	test udp
+	test valgrind
+	teardown passt_in_ns
+
+	VALGRIND=0
+	setup passt_in_ns
+	test ndp
+	test dhcp
 	test perf
 	teardown passt_in_ns