MEDIUM: Split up struct server's check element

This is in preparation for associating a agent check
with a server which runs as well as the server's existing check.

The split has been made by:
* Moving elements of struct server's check element that will
  be shared by both checks into a new check_common element
  of struct server.
* Moving the remaining elements to a new struct check and
  making struct server's check element a struct check.
* Adding a server element to struct check, a back-pointer
  to the server element it is a member of.
  - At this time the server could be obtained using
    container_of, however, this will not be so easy
    once a second struct check element is added to struct server
    to accommodate an agent health check.

Signed-off-by: Simon Horman <horms@verge.net.au>
MEDIUM: Move result element to struct check

Move result element from struct server to struct check
This allows check results to be independent of the check's server.

This is in preparation for associating a agent check
with a server which runs as well as the server's existing check.

Signed-off-by: Simon Horman <horms@verge.net.au>
MEDIUM: Paramatise functions over the check of a server

Paramatise the following functions over the check of a server

* set_server_down
* set_server_up
* srv_getinter
* server_status_printf
* set_server_check_status
* set_server_disabled
* set_server_enabled

Generally the server parameter of these functions has been removed.
Where it is still needed it is obtained using check->server.

This is in preparation for associating a agent check
with a server which runs as well as the server's existing check.
By paramatising these functions they may act on each of the checks
without further significant modification.

Explanation of the SSP_O_HCHK portion of this change:

* Prior to this patch SSP_O_HCHK serves a single purpose which
  is to tell server_status_printf() weather it should print
  the details of the check of a server or not.

  With the paramatisation that this patch adds there are two cases.
  1) Printing the details of the check in which case a
     valid check parameter is needed.
  2) Not printing the details of the check in which case
     the contents check parameter are unused.

  In case 1) we could pass SSP_O_HCHK and a valid check and;
  In case 2) we could pass !SSP_O_HCHK and any value for check
  including NULL.

  If NULL is used for case 2) then SSP_O_HCHK becomes supurfulous
  and as NULL is used for case 2) SSP_O_HCHK has been removed.

Signed-off-by: Simon Horman <horms@verge.net.au>
MEDIUM: cfgparse: Factor out check initialisation

This is in preparation for struct server having two elements
of type struct check.

Signed-off-by: Simon Horman <horms@verge.net.au>
MEDIUM: Add state to struct check

Add state to struct check. This is currently used to store one bit,
CHK_RUNNING, which is set if a check is running and clear otherwise.
This bit was previously SRV_CHK_RUNNING of the state element of struct
server.

This is in preparation for associating a agent check
with a server which runs as well as the server's existing check.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
MEDIUM: Move health element to struct check

This is in preparation for associating a agent check
with a server which runs as well as the server's existing check.

Signed-off-by: Simon Horman <horms@verge.net.au>