feat(dhcpcd): add /var/lib/dhcpcd writable-paths for datasource disco…

…very

If dhcpcd is installed in a cloud image, cloud-init may attempt early
datasource discovery using dhcpcd in order to get information about
active instance metadata service IP addresses and routes.
The dhcpcd client writes out leases which cloud-init parses under
/var/lib/dhcpcd.

Add this support so cloud-init can detect network-bound datasources such
as Azure, Ec2 and GCE.

static/etc/system-image/writable-paths

@@ -54,6 +54,7 @@
 /var/lib/apparmor                       auto                    persistent  transition  none
 /var/lib/dbus                           auto                    persistent  none        none
 /var/lib/dhcp                           auto                    persistent  none        none
+/var/lib/dhcpcd                         auto                    persistent  transition  none
 # cloud-init
 /etc/cloud                              auto                    persistent  transition  none
 /var/lib/cloud                          auto                    persistent  none        none