test: adds block refs for mock_cassandra

This patch adds block-reference counting ability to the cassndra mocker.
test: block reference counts

This patch adds tests for block reference counting. The scenarios
covered are checking block references incrementing and decrementing on
assignment to file and on deletion of the file.
feat(blockrefs): cassandra schema modification

This patch changes the cassandra schema to add a counter column family
to the schema file.
feat(blockrefs): adds base class

This patch adds the prototype to the base metadata driver class.
feat(blockrefs): mongo DB support

This patch adds basic block reference counting to the mongodb metatdata
storage driver.
feat(blockrefs): cassandra support

This patch adds basic block reference counting support to the cassandra
metadata storage driver.
feat(blockrefs): sqlite support

This patch adds basic block reference counting support to the sqlite
metadata storage driver
Merge remote-tracking branch 'upstream/master' into feat_block_ref_counting
chore: removes debugging artifact
Merge remote-tracking branch 'upstream/master' into check_merge

Conflicts:
	deuce/drivers/cassandra/cassandrametadatadriver.py
	deuce/drivers/metadatadriver.py
	deuce/drivers/mongodb/mongodbmetadatadriver.py
	deuce/drivers/sqlite/sqlitemetadatadriver.py
Merge pull request #98 from painterjd/feat_block_ref_counting

Basic Block Reference Counting
Merge remote-tracking branch 'repo/master' into 109_list_vault_2