conf: route service conditions through one owner primitive

A service's condition was computed with mkcond() at each of the six
sites that assert or clear it, and svc_find_by_cond() reimplemented
the reverse lookup a seventh time.  maybe_clear_cond() had its own
scan for another service supplying the same condition.

svc_cond_owner() answers who owns a condition, svc_cond_nth() walks
the conditions a service owns, and svc_cond_set()/svc_cond_clear()
apply to all of them.  svc_find_by_cond() becomes a wrapper, and
maybe_clear_cond() keeps its rule per condition rather than for the
one it used to compute.

The provides[] storage lands here unused, since svc_cond_nth() reads
num_provides.  Nothing sets it yet, so a service still owns exactly
its own pid/<ident> and there is no functional change.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/api.c

@@ -112,8 +112,6 @@ static int restart(svc_t *svc, void *user_data)
 
 static int reload(svc_t *svc, void *user_data)
 {
-	char cond[MAX_COND_LEN];
-
 	(void)user_data;
 
 	if (!svc)
@@ -138,7 +136,7 @@ static int reload(svc_t *svc, void *user_data)
 	 * mechanism which may not re-trigger on SIGHUP.
 	 */
 	if (svc_is_noreload(svc)) {
-		cond_clear(mkcond(svc, cond, sizeof(cond)));
+		svc_cond_clear(svc);
 		if (svc->notify == SVC_NOTIFY_PID || svc->notify == SVC_NOTIFY_NONE)
 			service_ready(svc, 0);
 	}