Testing: CLI integration tests

[woodruffw]

I got started on these in #321, but they need much more work. Each kbs2 subcommand should have an integration test suite, ideally covering all combinations of options.

The list:

• kbs2 (Initial integration tests #321)
• kbs2 init (Initial integration tests #321)
• kbs2 new (Initial integration tests #321)
• kbs2 config
• kbs2 agent
• kbs2 dump
• kbs2 edit
• kbs2 env
• kbs2 generate
• kbs2 help
• kbs2 list
• kbs2 pass
• kbs2 rekey
• kbs2 rewrap
• kbs2 rm