Limit the number of Redis connections maintained in the per sync process ConnectionPool. Also set a connection timeout.
Limit the number of Redis connections maintained in the per sync process ConnectionPool.
Also set a connection timeout.

Summary:
The MAX_CONNECTIONS constant is set by back-calculating from the number of sync processes
we have; the SOCKET_TIMEOUT has been picked somewhat arbitrarily.

Test Plan:
Tested manually.

Reviewers: khamidou, emfree

Reviewed By: emfree

Differential Revision: https://phab.nylas.com/D2302

nylas/sync-engine,jobscore/sync-engine,closeio/nylas,jobscore/sync-engine,nylas/sync-engine,closeio/nylas,jobscore/sync-engine,jobscore/sync-engine,nylas/sync-engine,nylas/sync-engine,closeio/nylas,closeio/nylas