s3:libads: change ads_add_service_principal_name implementation

s3:libads: change ads_add_service_principal_name implementation

Previously the function 'ads_add_service_principal_name' created
the SPNs based on the machine_name and dns name passed to the function.
In order to prepare for a future patch that will also need to write
SPN(s) to the AD computer account, the function implementation will
need to be changed. Instead of the function creating the SPN(s) it
will now take the list SPN(s) to write to the AD 'machine_name' account
as an input param instead.
The name of the function has been changed to
'ads_add_service_principal_names' to reflect this. Additionally  client
code now needs to construct the SPNs to be passed into the function.

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>