feat: fallback to "grandpa tables" 👴

[Carl Montanari]

launcher may fail to start docker service w/ zero info as to why. turns out could be because iptables version is not happy and we get stuff like:

failed to start daemon: Error initializing network controller: error obtaining controller instance: setting default policy to DROP in FORWARD chain failed:  (iptables failed: iptables --wait -t filter -P FORWARD DROP: iptables v1.8.9 (nf_tables):  CHAIN_ADD failed (Operation not supported): chain FORWARD

in docker logs.

can work around like:

[*]─[test-clab]─[/etc/init.d]
└──> update-alternatives --set iptables /usr/sbin/iptables-legacy
update-alternatives: using /usr/sbin/iptables-legacy to provide /usr/sbin/iptables (iptables) in manual mode

[*]─[test-clab]─[/etc/init.d]
└──> service docker start
Starting Docker: docker.

so can use this if we fail to launch docker the "regular" way.