Omit/clarify "No keypair found" message generated when signing a compiled module

[Connor Smith]

Is your feature request related to a problem? Please describe.
Several users have expressed confusion at the following message that wash emits when generating a new keypair:

{"keygen":"true","path":"/Users/user/.wash/keys/derp_module.nk","status":"No keypair found"}

Describe the solution you'd like
This is an informational/debug message that shouldn't be emitted by default. Or, if we think it should, we should replace the serialized JSON — which tends to look "scary" — with a very clear message. Something like:

"Info: No existing keypair for module found. Wash generated a new one at /path/to/key"

Describe alternatives you've considered
I'm open to different wording/solutions. I think it would be easy to improve the status quo