generic_stages: Fix a bug in _FilterBuildFromMoblab

_FilterBuildFromMoblab is to filter out builds for moblab board.
However, a bug in the code makes it filter out builds for all board.

url.find('moblab') is always evaluated as true unless 'moblab' is
found in the beginning of the url.

BUG=b:125038064
TEST=unittest

Change-Id: If28c42588bb85288756d898523169c8d838a7f33
Reviewed-on: https://chromium-review.googlesource.com/1490418
Commit-Ready: Ke Wu <mikewu@google.com>
Tested-by: Ke Wu <mikewu@google.com>
Reviewed-by: Keith Haddow <haddowk@chromium.org>
(cherry picked from commit 9e7e84f5355474c55ecc0671d2901a32c8794657)
Reviewed-on: https://chromium-review.googlesource.com/c/1493254
Commit-Queue: Ke Wu <mikewu@google.com>
diff --git a/cbuildbot/stages/generic_stages.py b/cbuildbot/stages/generic_stages.py
index fcbd3d4..26881f5 100644
--- a/cbuildbot/stages/generic_stages.py
+++ b/cbuildbot/stages/generic_stages.py
@@ -1117,7 +1117,7 @@
       True is the build should not be copied to this moblab url
     """
     bot_filter_list = ['paladin', 'trybot', 'pfq', 'pre-cq', 'tryjob']
-    if (url.find('moblab') and
+    if (url.find('moblab') != -1 and
         any(bot_id.find(filter) != -1 for filter in bot_filter_list)):
       return True
     return False