Handle plots create default arguments

[altendky]

Draft for:

• Self testing
• Maybe just throw this out and figure out proper use of chia's own parser. Though, there hasn't been official agreement on making a hard expectation that there is a chia installed in the same env as plotman and that is the one in use. Though not requiring that kind of just leaves us hoping that we're matching.

[altendky]

If we decide against #116 then we can reconsider this.