cli.py: move timing check back to top
cli.py: move timing check back to top

We care about how long it takes to import all the wormhole-specific things,
to investigate user-perceived latency from the time the command is launched
to the time they can actually interact with it. So we need to record
`time.time()` before doing the rest of the imports, even though pep8 says all
imports should be done before any non-importing statements.

warner/magic-wormhole,warner/magic-wormhole,warner/magic-wormhole,warner/magic-wormhole