cli: agent --labels for overriding labels
master api, client: support label filtering

Some client commands now take --labels option.

- /agents, mamiya client list-agents
- /packages/:app/:pkg/distribution, mamiya client show-distribution

= Label expression

"foo" -> foo
"foo,bar" -> foo&&bar
"foo|baz" -> foo||baz
"foo,bar|baz" (foo&&bar)||baz
mamiya client distribute: support --labels