test-ovn: Use literal -1 instead of WAIT_ANY.

POSIX does not specify WAIT_ANY and at least MUSL libc does not define it.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

tests/test-ovn.c

@@ -983,7 +983,7 @@ wait_pid(pid_t *pids, int *n)
     int status;
     pid_t pid;
 
-    pid = waitpid(WAIT_ANY, &status, 0);
+    pid = waitpid(-1, &status, 0);
     if (pid < 0) {
         ovs_fatal(errno, "waitpid failed");
     } else if (WIFEXITED(status)) {