Make crutest's volume create error out when conflicts arise

[leftwo]

Right now you can specify:
Various crucible opts.
A dsc endpoint
A VCR file

Some of these options will conflict and or take precedence over each other and it may
not be clear to the user what kind of volume they are getting.

Options that conflict should not be allowed, or should return error if they are detected.

[leftwo]

As we transition to supporting dsc for the tests in tools, we could take out the default values
for the opts that build CrucibleOpts and make those Option, which would enable us to enforce
some of this at the start.

Also, we should figure out how to handle multiple sub-volumes with different extent size/count.
dsc itself does not support creating them yet, but can be tricked into starting them.