Temporarily disable Karma tests on Windows CI

We are observing frequent test failures on Windows CI, where PhantomJS
cannot start because there are no free handles available. Finding
and fixing the process leaking handles is non-trivial and will take
long time.

This commit disables Karma tests on Windows CI machines to prevent
build failures that we are ignoring anyways.

Author: bajtos

Gruntfile.js

@@ -224,6 +224,10 @@ module.exports = function(grunt) {
     });
   });
 
+  grunt.registerTask('skip-karma-on-windows', function() {
+    console.log('*** SKIPPING PHANTOM-JS BASED TESTS ON WINDOWS ***');
+  });
+
   grunt.registerTask('e2e', ['e2e-server', 'karma:e2e']);
 
   // Default task.
@@ -233,7 +237,9 @@ module.exports = function(grunt) {
     'jscs',
     'jshint',
     process.env.JENKINS_HOME ? 'mochaTest:unit-xml' : 'mochaTest:unit',
-   'karma:unit-once']);
+    process.env.JENKINS_HOME && /^win/.test(process.platform) ?
+      'skip-karma-on-windows' : 'karma:unit-once',
+  ]);
 
   // alias for sl-ci-run and `npm test`
   grunt.registerTask('mocha-and-karma', ['test']);