Build: Use grep to filter test cases.

* Uses different strategy to test binary.
* Test two cases and declare the binary OK.
Issue URL: sass#611.

scripts/build.js

@@ -115,33 +115,23 @@ function testBinary(options) {
     return build(options);
   }
 
-  if (process.env.SKIP_NODE_SASS_TESTS) {
-    return;
-  }
-
   fs.stat(path.join(__dirname, '..', 'vendor', options.bin, 'binding.node'), function (err) {
     if (err) {
       return build(options);
     }
 
     console.log('`' + options.bin + '` exists; testing');
 
-    var total;
-    var failures;
     var mocha = new Mocha({
       ui: 'bdd',
-      timeout: 999999,
-      reporter: function(stats) {
-        total = stats.total;
-        failures = stats.failures;
-      }
+      timeout: 999999
     });
 
     mocha.addFile(path.resolve(__dirname, '..', 'test', 'api.js'));
-    mocha.run(function () {
-      if ((total - failures) * 100 / total < 90) {
+    mocha.grep(/should compile sass to css with file/).run(function (done) {
+      if (done !== 0) {
         console.log([
-          'Problem with the binary: ' + failures + ' of ' + total + ' tests are failing.',
+          'Problem with the binary.',
           'Manual build incoming.',
           'Please consider contributing the release binary to https://github.com/sass/node-sass-binaries for npm distribution.'
         ].join('\n'));