feat: storage block id prefixed with blockid(sha1)

The storage block id is now prefixed with the actual sha1 of the
blockdata. i.e block id

Some of the benefits:

1.We no longer need to query metadata to find the block id for the
corresponding storage id.
2. A performance boost for validation and cleanup service
3. Easy identification of oprhaned blocks if there is more than one
block that begins with the same sha1 in storage.
fix: separator must be '&' or ';'

- pep8 fix
- rename a test correctly
fix: simplify checking of separators
bugfix: os.listdir() is not sorted

explicitly sort, before applying marker or limit logic
feat: separation - endpoints for finalize & assign

finalize at:
    POST /v1.0/vaults/{vaultid}/files/{fileid}
assign at:
    POST /v1.0/vaults/{vaultid}/files/{fileid}/blocks
Merge remote-tracking branch 'upstream/master' into prefixsha1_storageid

Conflicts:
	deuce/drivers/blockstoragedriver.py
Support update to assign/finalize file endpoint
Merge pull request #195 from TheSriram/prefixsha1_storageid

feat: storage block id prefixed with blockid(sha1)
Merge remote-tracking branch 'upstream/master' into separate_endpoint_assingn_finalize

Conflicts:
	deuce/tests/test_files.py
Merge pull request #199 from TheSriram/separate_endpoint_assingn_finalize

feat: separation - endpoints for finalize & assign
Merge pull request #203 from jc7998/assign

API Test: Support update to assign/finalize file endpoint