MB-9883: allow asking for rc4-128 cipher

I.e. so that we can investigate that faster cipher influence of
overall cpu consumption.

Change-Id: I290e66ff17318f6d81aed1985493eeb32cc2b7ce
Reviewed-on: http://review.couchbase.org/32372
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>