[ale] Perform blocking operations on a separate process.

Change-Id: I7bc05c81f726d5b8cf7a476f53e5bf5976552aa2
Reviewed-on: http://review.couchbase.org/37805
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>