Standardize output format of meshctl commands

[jenshu]

The meshctl commands currently print the output in different formats, e.g. meshctl version outputs a pretty-printed json string, meshctl describe shows a table, meshctl check shows a list, etc. We should standardize the output format(s) and/or allow the user to choose.

We might want to do something similar to gloo: https://github.com/solo-io/gloo/blob/master/projects/gloo/cli/pkg/printers/printers.go