Quickstart: better errors

[josibake]

• If a user tries to create a custom directory with the same name as an already copied example, we should warn them. Currently it just barfs a stack trace

[pinheadmz]

also we should make sure we exit early if the user does NOT want to create a custom network:

[willcl-ark]

Isn't this fixed by #563?

[pinheadmz]

looks like #563 indeed fixes my error in the screenshot, what about Josie's in the OP though?

[josibake]

what about Josie's in the OP though?

this still needs fixed

[mplsgrant]

This appears fixed to me. Am I missing an edge case?