Validate that run-bindings-tests is testing results.

Currently, RBT doesn't generate files in a temp directory in /tmp.  Instead idl_compiler is using format string to build a file name however the output_directory doesn't end with a slash (all files are /tmp/tmpXXXXV8nnnnn.h or .cpp).  Should use path join to construct file name.

Also, fixed no_excess_files to check both Perl's output directory and Python's output directory (was only checking Perl output directory).

R=nbarth@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/179993004

git-svn-id: svn://svn.chromium.org/blink/trunk@167837 bbb929c8-8fbe-4397-9dbb-9b2b20218538