Add basic tests for ctfconvert(1), fold(1) and rs(1)

Add basic command line parsing test coverage for these utilities. The tests
were automatically generated based on their man pages. These tests can be
expanded by hand for more thorough coverage. The aim is to generate very
basic amount of test coverage for all the utilities in the base system.

Tests generated via: https://github.com/shivansh/smoketestsuite/

Submitted by: shivansh
Reviewed by: asomers
MFC after: 3 weeks
Differential Revision: https://reviews.freebsd.org/D12424