autopilot/agent: distribute available funds among channels
autopilot/agent: distribute available funds among channels

This commit fixes a regression in how we allocate funds to attempted
channels. We would earlier stay within the channel size limits, but we
wouldn't account for funds consumed by other channels being opened in
parallel.

We fix this by introducing a loop which greadily tries to distribute the
funds among the channels to open, and reduces the number of channels to
open in case not enough funds are available to satisfy the channel size
limits.

LightningNetwork/lnd,LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd