Add deprecation warnings for aurora client v1 command.

This change only touches the commands in the "core" set, defined in
core.py. If reviewers approve of this approach, I'll make similar changes to
the other v1 commands in a subsequent review.

Testing note: unit tests for this don't seem appropriate: this is
temporary code that doesn't actually affect the behavior of the system.
Human verification that the alternative v2 commands in the deprecation
messages is the only way to ensure that they're correct.

A couple of examples of the generated messages:

$ ./dist/aurora2.pex update --shards=1-3  example/mchucarroll/test/bozo examples/jobs/hello_world.aurora
WARNING: update is an aurora clientv1 command which will be deprecated soon
To run this command using clientv2, use 'aurora job update example/mchucarroll/test/bozo/1,2,3 examples/jobs/hello_world.aurora --health-check-interval-seconds=3'

$ /dist/aurora2.pex kill --shards=1-3  example/mchucarroll/test/bozo examples/jobs/hello_world.aurora
WARNING: kill is an aurora clientv1 command which will be deprecated soon
To run this command using clientv2, use 'aurora job kill example/mchucarroll/test/bozo/1,2,3 --config=examples/jobs/hello_world.aurora --max-total-failures=1'

./dist/aurora2.pex create --open_browser  example/mchucarroll/test/hello examples/jobs/hello_world.aurora
WARNING: create is an aurora clientv1 command which will be deprecated soon
To run this command using clientv2, use 'aurora job create example/mchucarroll/test/hello examples/jobs/hello_world.aurora --open-browser'

Bugs closed: aurora-131

Reviewed at https://reviews.apache.org/r/24160/