itest: add new RBF coop close itest

The itest has both sides try to close multiple times, each time with
increasing fee rates. We also test the reconnection case, bad RBF
updates, and instances where the local party can't actually pay for
fees.

itest/lnd_coop_close_with_htlcs_test.go

@@ -66,7 +66,6 @@ func testCoopCloseWithHtlcs(ht *lntest.HarnessTest) {
 // channel party initiates a channel shutdown while an HTLC is still pending on
 // the channel.
 func coopCloseWithHTLCs(ht *lntest.HarnessTest, alice, bob *node.HarnessNode) {
-
 	ht.ConnectNodes(alice, bob)
 
 	// Here we set up a channel between Alice and Bob, beginning with a