fixed misc.erl tests to not leave messages in process mailbox

Change-Id: I22c99ef203dd52fd5d754254277d7a31451931ca
Reviewed-on: http://review.couchbase.org/38985
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>