daemon: deglobalize hostname information

daemon: deglobalize hostname information

Move the variables related to the client-supplied hostname into its own
struct, let execute() own an instance of that instead of storing the
information in global variables and pass the struct to any function that
needs to access it as a parameter.

The lifetime of the variables is easier to see this way.  Allocated
memory is released within execute().  The strbufs don't have to be reset
anymore because they are written to only once at most: parse_host_arg()
is only called once by execute() and lookup_hostname() guards against
being called twice using hostname_lookup_done.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>