Fix ninja tests if NINJA_STATUS is set
Fix ninja tests if NINJA_STATUS is set

If NINJA_STATUS is set in the environment when running runtest.rb -c -n
the regexp to match ninja status lines may not match, causing all the
tests to fail.  Set NINJA_STATUS to a known value that is easy to match
for.

Change-Id: Ice892341a252ca305f770d5c92d9716ee857156b

google/kati,danw/kati,danw/kati,shinh/kati,shinh/kati,danw/kati,google/kati,danw/kati,google/kati,shinh/kati,shinh/kati,shinh/kati,danw/kati,google/kati,shinh/kati,danw/kati,google/kati