git node land simplifications

It should be possible to anticipate the next command. For example in case a rebase is needed due to multiple commits. In such case, it would be nice to already execute the command that is currently printed to the terminal:

There are 3 commits in the PR
Please run the following commands to complete landing

$ git rebase origin/master -i -x "git node land --amend"
$ git node land --continue

It would be good to already run git rebase origin/master -i -x "git node land --amend". Even git node land --continue should be possible to run automatically as soon as that's done.

Removing the temporary files should also be done by default. A user might opt out by a config flag instead?