ds-identify: override environment variables on FreeBSD

override PATH_DI_CONFIG and PATH_ETC_CLOUD when executing ds-identify \
on startup.

Inconviniently, we can't just override PATH_ROOT, because that would set
/run to /usr/local/run and /var/lib/cloud to /usr/local/var/lib/cloud.

In the future we will want to override /run, but we can't do that just
yet without also ensuring that the python code can relocate /run.

Fixes: GH-4481
Sponsored by: The FreeBSD Foundation

sysvinit/freebsd/dsidentify.tmpl

@@ -39,5 +39,6 @@ load_rc_config 'cloudinit'
 
 : ${cloudinit_enable="NO"}
 : ${cloudinit_dsidentify_enable="YES"}
+: ${cloudinit_env"PATH_DI_CONFIG={{ prefix }}/etc/cloud/ds-identify.cfg PATH_ETC_CLOUD={{ prefix }}/etc/cloud"}
 
 run_rc_command "$1"