libs/libhutils/*: fix confusing wait_chdl_[timed] () return value

Now, hutils_wait_chld () returns, on successfully
waiting a child, its PID number, instead of 0.
This gives the ability to other functions to
distinguish between "nothing to wait for" from
"successfully waited child".

src/libs/libhutils/src/hutils_utils.c

@@ -245,7 +245,7 @@ int hutils_wait_chld (void)
                 WTERMSIG(chld_status));
     }
 
-    return 0;
+    return chld_pid;
 }
 
 int hutils_wait_chld_timed (int timeout)
@@ -260,7 +260,7 @@ int hutils_wait_chld_timed (int timeout)
         }
 
         err = hutils_wait_chld ();
-        if (err == 0) {
+        if (err > 0) {
             DBE_DEBUG (DBG_HAL_UTILS | DBG_LVL_WARN, "[hutils:utils] "
                     "hutils_wait_chld_timed: finished waiting\n");
             goto exit;