Bug Fix Block Size

- Enforce that the specified size of the data matches the actual size of the data when adding a block
- Fix the block put end-point to correctly get the content length even if the caller forgot to specify it so that we have it for the validation (above) and database if everything matches
Bug Fix - store_async_block

- Swift Driver: API Contract changed and failure case was not updated to reflect the new contract
--- updated failure case for the new contract so it doesn't break the up-level code when failure occurs
--- updated the failure test for the new contract
- Disk Driver: There was no possible way for it to fail even if it failed to write a block
--- Had to remove the contextual file open as it was prevent 100% test coverage, documented it in the code
--- Added a specific test case that is skipped for the swift driver as it only applies to the disk driver to test the disk driver's failure case
Bug Fixes

- Bug Fix (Cassandra): Only insert the reftime when we actually have a block in storage since we store the reftime with the block data
- Bug Fix (DiskStorageDriver): store_block must be able to fail
- Bug Fix (BlockStorageDrivers): store_block failure values must match the structure of the success values
Notes

- Added a couple comments regarding why something is being done
Pep8 Compliance & more documentation

- Bug Fix (CassandraStorageDriver) - pep8 compliance
- Documentation (test_disk_storage_driver) - added notes about why we use open_values() the way we do in the two sections for testing store_block() and store_async_block()
Enhancement: Little bit better error handling

- Ensure the file is closed properly when an error occurs
Bug Fix

- Coverage was being inconsistent on line 30; this may be in part due to the how the self._current_file was being initialized.
--- this fixes it so that self._current_file is always initialized to something, so it exists, but we only set it something else when the correct conditions are met
Merge pull request #206 from BenjamenMeyer/bugfix_block_size

Bug Fix Block Size