add missing host_app check in sharding for iOS test runner

host_app defaults to 'NO_PATH' via run.py, but the check doesn't
include this in shard_utils.py. Including this check and printing
the host_app in this logic.

This only is triggered for gtest_type tests for iOS that are
sharded by Swarming, thus, having those environment variables set.

Change-Id: If9cfcb707866e23ef416ee6be32b54dd48eb7910
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2045375
Commit-Queue: Jeff Yoon <jeffyoon@chromium.org>
Auto-Submit: Jeff Yoon <jeffyoon@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743172}

ios/build/bots/scripts/shard_util.py

@@ -52,8 +52,9 @@ def determine_app_path(app, host_app=None):
   # Default app_path looks like /b/s/w/ir/out/Debug/test.app/test
   app_path = os.path.join(full_app_path, app_name)
 
-  if host_app:
-    LOGGER.debug("Detected EG2 test while building application path.")
+  if host_app and host_app != 'NO_PATH':
+    LOGGER.debug("Detected EG2 test while building application path. "
+                 "Host app: {}".format(host_app))
     # EG2 tests always end in -Runner, so we split that off
     app_name = app[:app.rindex('-Runner')]
     app_path = os.path.join(full_app_path, 'PlugIns',