Fix brittle command tests

#### Summary:

Makes command tests more robust to minor changes in output.

#### Intended Effect:

Reduces the developer's need to change the command tests each time the output changes a little bit.

#### How to Verify:

Run: `make test/CmdStan/command`

#### Side Effects:

None.

#### Documentation:

None.

#### Reviewer Suggestions:

Anyone. This is a change to the tests only.