[autotest] Improve pool health bugs

Assign and label pool health bugs appropriately, and add more detailed
host information to the bug.

BUG=chromium:637008
TEST=Run run_suite.py with fewer hosts than required, run unittests

Change-Id: I801b8bfb028a9a576d48fecda017c439b93088fe
Reviewed-on: https://chromium-review.googlesource.com/372879
Commit-Ready: Allen Li <ayatane@chromium.org>
Tested-by: Allen Li <ayatane@chromium.org>
Reviewed-by: Allen Li <ayatane@chromium.org>
diff --git a/server/site_utils.py b/server/site_utils.py
index d5da31a..2e4a66b 100644
--- a/server/site_utils.py
+++ b/server/site_utils.py
@@ -178,6 +178,7 @@
     return None
 
 
+# TODO(fdeng): fix get_sheriffs crbug.com/483254
 def get_sheriffs(lab_only=False):
     """
     Polls the javascript file that holds the identity of the sheriff and