STITCH-1958 - Implement atomic sync operations

[edaniels]

General algorithm and implementation status:
For each operation
1. Take out a collection level (NS) lock (done)
2. For reads
2a. do a normal read and release the lock (done)
3. For writes
3a. find documents to be affected (done)
3b. Write the documents to an undo collection (done)
3c. do the write to the local collection (done)
3d. mark the document config as having an uncommitted write (done)
3e. remove the undo document (done)
4. Unlock the collection level lock (done)

For sync
1. For each namespace to synchronize, take out a lock when wanting to making read/writes on doc configs/local collection (done)

On DataSynchronizer startup
1. Lock the NS and dispatch a request to do the below (done)
2. Search for any undo documents (done)
3. Replace the local database version of the document with the undo document (done)
4. Set difference of local docs and configs. Remove difference from local docs (done)
5. Unlock the NS (done)

Drive-bys:

• insertOneAndSync -> insertOne
• insertManyAndSync -> insertMany
• Remove Server version of Sync
• Stop publishing Server version local MongoDB service

[coveralls]

Coverage decreased (-43.3%) to 27.5% when pulling 82e40da on edaniels:STITCH-1958 into ee20789 on mongodb:master.

[coveralls]

Coverage decreased (-5.08%) to 66.833% when pulling 48460af on edaniels:STITCH-1958 into 7c836d0 on mongodb:master.

[jsflax]

This LGTM! Great job. I imagine it might be tough to write an integration test for this, but it would be nice to see a unit test or two to test the recovery functionality.

[adamchel]

This looks great! Couple nits and q's, and I agree with Jason that a test would be nice.

[dkaminsky]

lgtm