dynamic-dns: T2528: bugfix FileNotFoundError in "update dns dynamic"
dynamic-dns: T2528: bugfix FileNotFoundError in "update dns dynamic"

Stopping and starting ddclient should only happen if the DNS dynamic service
is actually configured. In addition it should always be checked if the file
we try to delete really exists.

vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x,vyos/vyos-1x