DATAREST-387 - Added integration tests for Spring Data Solr repositories.

Added configuration for setting up an EmbeddedSolrServer instance within a temporary directory. We use a temporary test folder created by JUnit where we copy the required configuration to. The directory will also hold all index data and will be deleted afterwards.

Original pull request: #156.
DATAREST-387 - Separated integration tests for individual stores.

Original pull request: #156.