lnd_test: use dave to listen for ChannelUpdates in testSendUpdateDisableChannel
lnd_test: use dave to listen for ChannelUpdates in testSendUpdateDisableChannel

This commit changes the test testSendUpdateDisableChannel to use Dave to
listen for channel updates, as was originally intended.

Since a ChannelUpdate won't propagate in the network if the channel is
already closed (if the closing transaction has been mined), we change
the closing procedure to initiate the closing process, wait for the
ChannelUpdates, then finally mining the closing transaction. This avoids
a propagation race between the mined block and the ChannelUpdate.

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