Fix OPENDJ-734 - NPE when attempting SSL connect with client certs
Review CR-1243

NPE happens when no trust password is given.

* ConnectionFactoryProvider.java : 
  - test for null value before converting to charArray
  - fixed a unrelated copy-paste error (using trustStorePathArg instead of keyStorePathArg)

* Added a test class ConnectionFactoryProviderTest.java to check behavior in case no trust password is given
* Added a dummy-trustore in test resources, as this is needed for correct behavior of tested method getConnectionFactory