This commit fixes a flake in the channel status update itest that
occurred if Carol got a channel edge update for a channel before it
heard of the channel in the first place. To avoid that, we wait for
Carol to sync her graph before sending out channel edge or policy
updates.
As always when we touch itest code, we bring the formatting and use of
the require library up to date.
In this commit, we put the context initialization inside
openChannelAndAssert, thus saving us a few lines and making sure the
context is always properly handled.
