downgrading lightningd 0.12.1 to 0.11.1

[eoliveros]

using the following instructions, i was able to downgrade from 0.12.1 to 0.11.1:

- stop lightningd
- cp -r /opt/ln_data /opt/ln_data-bak
- delete /opt/ln_data/*
- delete lightningd container
- delete lightningd image
- build image
- start image(just enough to build the files in /opt/ln_data)
- stop lightningd
- cp hsm_secret from ln_data-bak/ file to /opt/ln_data/testnet/ (if we want to use the old hsm_secret)
- build image(might not be needed)
- start lightningd

[djpnewton]

testing on be.bitforge.me