This is a WIP patch to add a feature to add gtm_proxy on the fly.

This is also a preliminary work to add coordinator/datanode slave
on the fly.

	modified:   contrib/pgxc_ctl/config.c
	modified:   contrib/pgxc_ctl/config.h
	modified:   contrib/pgxc_ctl/gtm_cmd.c
	modified:   contrib/pgxc_ctl/gtm_cmd.h
	modified:   contrib/pgxc_ctl/signature.h
	modified:   contrib/pgxc_ctl/variables.h