Refactored fixity workers.

[bb233]

I have refactored the fixity workers to make the code between the S3 and SFS workers exist in a common class, and only S3/SFS-specific details are implemented in the individual classes.

To implement a new fixity worker type, you just need to implement the three methods:

• worker_type, which returns the manifest-type specific suffix (S3, SFS, Ingest) used in the manifest file name,
• object_key_paths(msg), which returns a hash of object keys and paths to be included in the manifest
• calculate_checksum(path), which calculates the SHA1 hexdigest for a path.

[coveralls]

Pull Request Test Coverage Report for Build 72

• 34 of 37 (91.89%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.3%) to 91.982%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
lib/archival_storage_ingest/workers/fixity_worker.rb	32	35	91.43%
<!--	Total:	34	37	91.89%	-->

Totals
Change from base Build 67:	-0.3%
Covered Lines:	826
Relevant Lines:	898

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 70

• 34 of 37 (91.89%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.3%) to 91.982%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
lib/archival_storage_ingest/workers/fixity_worker.rb	32	35	91.43%
<!--	Total:	34	37	91.89%	-->

Totals
Change from base Build 67:	-0.3%
Covered Lines:	826
Relevant Lines:	898

---

💛 - Coveralls