trivial: fix whitespace-linter catching false positives

Ignores .pyc files and files contained in htmlcov as a coverage
job was recently added.

Change-Id: I33b1b88e90060f3b26f41b6acbbc0c7091caeb57

tools/gate/whitespace-linter.sh

@@ -5,7 +5,9 @@ RES=$(find . \
   -not -path "*/\.*" \
   -not -path "*/doc/build/*" \
   -not -path "*/doc/source/images/*" \
+  -not -path "*/htmlcov/*" \
   -not -name "*.tgz" \
+  -not -name "*.pyc" \
   -type f -exec egrep -l " +$" {} \;)
 
 if [[ -n $RES ]]; then