tests: Fix conntrack not being flushed between tests.

Since the split, the conntrack is no longer flushed between system
tests.  This may cause some random failures if residual conntrack
entries interfere with the next test in some way.  The command doesn't
exist in the OVN's ovstest.  The one from OVS should be used instead:

  ovstest: unknown command 'test-netlink-conntrack'; use --help for help

Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Signed-off-by: Dumitru Ceara <dceara@redhat.com>
(cherry picked from commit f12c8a2)

tests/automake.mk

@@ -92,6 +92,7 @@ MULTINODE_TESTSUITE_RESULTS = $(MULTINODE_TESTSUITE_DIR)/results
 AUTOTEST_PATH = $(ovs_builddir)/utilities:$(ovs_builddir)/vswitchd:$(ovs_builddir)/ovsdb:$(ovs_builddir)/vtep:tests:$(PTHREAD_WIN32_DIR_DLL):$(SSL_DIR):controller-vtep:northd:utilities:controller:ic
 
 export ovs_srcdir
+export ovs_builddir
 
 check-local:
 	set $(SHELL) '$(TESTSUITE)' -C tests AUTOTEST_PATH=$(AUTOTEST_PATH); \

tests/system-kmod-macros.at

@@ -68,7 +68,7 @@ m4_define([CHECK_CONNTRACK],
                  on_exit 'modprobe -r mod'
                 ])
      sysctl -w net.netfilter.nf_conntrack_helper=0
-     on_exit 'ovstest test-netlink-conntrack flush'
+     on_exit "${ovs_builddir}/tests/ovstest test-netlink-conntrack flush"
 )
 
 # CHECK_CONNTRACK_ALG()