To avoid needing to support all possible configuration options in the Guix
service.
* gnu/services/guix.scm
(guix-build-coordinator-configuration-extra-build-coordinator-arguments): New
procedure.
* gnu/services/guix.scm (make-guix-build-coordinator-start-script): Support
extra-build-coordinator-arguments and include them when calling
make-build-coordinator.
(guix-build-coordinator-shepherd-services): Pass
extra-build-coordinator-arguments through when calling
make-guix-build-coordinator-start-script.
Change-Id: I6531275bf2922f762b3422746c6207b834656b5c