cros_workon_make: make sure P2 vars get reset between runs

We don't want values from previous runs sticking around if the user
hasn't set them, so add these platform2 vars to the clean list.

BUG=None
TEST=precq passes

Change-Id: Ia644063145296b082c04d084bc95f0b20c0b4a74
Reviewed-on: https://chromium-review.googlesource.com/719676
Commit-Ready: Lutz Justen <ljusten@chromium.org>
Tested-by: Lutz Justen <ljusten@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
Reviewed-by: Lutz Justen <ljusten@chromium.org>
diff --git a/host/cros_workon_make b/host/cros_workon_make
index bb896d1..4e58268 100755
--- a/host/cros_workon_make
+++ b/host/cros_workon_make
@@ -99,6 +99,9 @@
   CROS_WORKON_MAKE_COMPILE_ARGS
   # Common test vars.
   GTEST_ARGS
+  # Platform eclass vars.
+  P2_TEST_FILTER
+  P2_VMODULE
 )
 
 # Determine if we're going to do tests, set up commands appropriately.