http: set named susbsytem to "capi/mgmt".

Helps us identify these types of connections better in the logs

Change-Id: I01870af7cf3610529b0cf00deaae9e2f6856227d
Reviewed-on: http://review.couchbase.org/37859
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>