ds-identify: Allow disable service and override environment (#4485)

This PR allows disabling the ds-identify service on FreeBSD, without
having to delete the service file.
It also overrides two environment variables when running the service
to ensure that on FreeBSD, paths are where they are to be expected.

Fixes GH-4481
Sponsored by: The FreeBSD Foundation
Co-authored-by: Dave Cottlehuber <dch@skunkwerks.at>

sysvinit/freebsd/dsidentify.tmpl

@@ -23,18 +23,22 @@ rcvar="cloudinit_enable"
 
 dsidentify_start()
 {
-    echo "${command} starting"
-    if kenv -q kernel_options | grep -q 'cloud-init=disabled'; then
-        warn "cloud-init is disabled via kernel_options."
-    elif test -e {{ prefix }}/etc/cloud-init.disabled; then
-        warn "cloud-init is disabled via cloud-init.disabled file."
-    else
-        ${command}
+    if checkyesno cloudinit_dsidentify_enable; then
+        echo "${command} starting"
+        if kenv -q kernel_options | grep -q 'cloud-init=disabled'; then
+            warn "cloud-init is disabled via kernel_options."
+        elif test -e {{ prefix }}/etc/cloud-init.disabled; then
+            warn "cloud-init is disabled via cloud-init.disabled file."
+        else
+            ${command}
+        fi
     fi
 }
 
 load_rc_config 'cloudinit'
 
 : ${cloudinit_enable="NO"}
+: ${cloudinit_dsidentify_enable="YES"}
+: ${dsidentify_env="PATH_DI_CONFIG={{ prefix }}/etc/cloud/ds-identify.cfg PATH_ETC_CLOUD={{ prefix }}/etc/cloud"}
 
 run_rc_command "$1"