Control debug verbosity with --debug-mixins or --verbosity

[carolynvs]

We really cleaned up the default info shown when we moved debugging for plugin communication to --debug-plugins. Would it help to have the same flag for mixins?

That way when someone runs porter build --debug they don't have the output overrun by stuff like this:

/var/folders/c9/s6tp7cv577d7j22pk0xg80qc0000gn/T/porter019480405/mixins/exec/exec version --output json --debug
DEBUG name:    helm
DEBUG pkgDir: /var/folders/c9/s6tp7cv577d7j22pk0xg80qc0000gn/T/porter019480405/mixins/helm
DEBUG file:
DEBUG stdin:

/var/folders/c9/s6tp7cv577d7j22pk0xg80qc0000gn/T/porter019480405/mixins/helm/helm version --output json --debug
DEBUG name:    kubernetes
DEBUG pkgDir: /var/folders/c9/s6tp7cv577d7j22pk0xg80qc0000gn/T/porter019480405/mixins/kubernetes
DEBUG file:
DEBUG stdin:

/var/folders/c9/s6tp7cv577d7j22pk0xg80qc0000gn/T/porter019480405/mixins/kubernetes/kubernetes version --output json --debug
DEBUG name:    terraform
DEBUG pkgDir: /var/folders/c9/s6tp7cv577d7j22pk0xg80qc0000gn/T/porter019480405/mixins/terraform
DEBUG file:
DEBUG stdin:

# TRUNCATED

Alternatively we could switch to a verbosity level, and have the default level filter out stuff like that. For example:

porter build --verbosity|v 1-5

1. Errors only (essentially --silent if we had that)
2. Only output from bundle calls itself, like if the mixin prints helm status, and required output from calls like porter schema or porter installation show porter-hello
3. Print task callouts from porter, e.g. "Building bundle", or "Running step Install World"
4. Print docker build output and output of commands run that normally we are just capturing and scraping
5. Print mixin and plugin debug lines

[carolynvs]

I'm really leaning towards a single verbosity flag, with friendly names for the numbers. So a user wouldn't need to remember what 4 is. The default verbosity would be normal (2).

$ porter build -v silent|0
never print, just execute and communicate status via exit code

$ porter build -v errorsonly|1
only print errors

$ porter build -v normal|2
print bundle output from porter install, the json from porter schema, and requested output from other commands like porter installation show

$ porter build -v tasks|3
Include porter and mixins output about what task it is doing, e.g. "building invocation image"

$ porter build -v commands|4
Show command and its output, e.g. the docker build output, helm mixin calling helm install with its output

$ porter build -v communication|5
Print all the extra debug lines we have for communicating with the mixins and plugins