last refactoring of tests provides reason the tests are failing

Provides nice output such as:

```text
1) OAuth2\Storage\ClientTest::testGetClientDetails with data set #5 (Cassandra)
Skipped Storage: Unable to connect to cassandra server on "127.0.0.1:9160"

2) OAuth2\Storage\PublicKeyTest::testSetAccessToken with data set #5 (Cassandra)
Skipped Storage: Missing cassandra library. Please run "composer.phar require thobbs/phpcassa:dev-master"

3) OAuth2\Storage\ClientTest::testSaveClient with data set #3 (Mongo)
Skipped Storage: Unable to connect to mongo server on "localhost:27017"

4) OAuth2\Storage\RefreshTokenTest::testSetRefreshToken with data set #3 (Mongo)
Skipped Storage: Missing mongo php extension. Please install mongo.so

5) OAuth2\Storage\AccessTokenTest::testSetAccessToken with data set #4 (Redis)
Skipped Storage: Unable to connect to redis server on port 6379

6) OAuth2\Storage\UserCredentialsTest::testCheckUserCredentials with data set #4 (Redis)
Skipped Storage: Missing redis library. Please run "composer require predis/predis:dev-master"
```

This should help contributors be able to run the test suite and determine why tests are being skipped