Bug 1312739 - Fix marionette SEARCH_PATHS in mach_test_package_bootstrap.py, r=jmaher

In bug 1320073, the marionette package structure was refactored a bit. This made the SEARCH_PATHS
in the mach test package bootstrap outdated. While this didn't end up causing any errors due to
marionette also appearing in an activated virtualenv, it should still be fixed. Figured since I was
in the area, I would just piggy-back off this commit series rather than filing a new bug.

MozReview-Commit-ID: DCNz3xEVJfY

--HG--
extra : rebase_source : 5f019d2ca80e008e89c8b9bc93722534f103a58c

testing/tools/mach_test_package_bootstrap.py

@@ -12,8 +12,8 @@ import types
 
 
 SEARCH_PATHS = [
-    'marionette',
-    'marionette/marionette/runner/mixins/browsermob-proxy-py',
+    'marionette/harness',
+    'marionette/harness/marionette_harness/runner/mixins/browsermob-proxy-py',
     'marionette/client',
     'mochitest',
     'mozbase/manifestparser',