Tell NPM to put its build cache inside $HOME/coursebuilder_resources_...

By default, npm caches into $HOME/.npm.  We want CB to be as self-contained
and non-interfering as possible, so have the npm cache be with the rest of
the Course Builder resources
	Change on 2015/12/09 by mgainer <mgainer@google.com>
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=109805104

coursebuilder/scripts/common.sh

@@ -216,7 +216,7 @@ if need_install node ChangeLog Version 0.12.4 ; then
   rm node-download.tgz
   echo Installing Karma
   pushd $RUNTIME_HOME/node
-  ./bin/npm install jasmine-core@2.3.4 phantomjs@1.9.8 karma@0.12.36 \
+  ./bin/npm --cache $RUNTIME_HOME/node/cache install jasmine-core@2.3.4 phantomjs@1.9.8 karma@0.12.36 \
       karma-jasmine@0.3.5 karma-phantomjs-launcher@0.2.0 karma-jasmine-jquery \
       --save-dev
   popd