add tests for rrdesi and rrboss

[sbailey]

redrock unit tests currently test the algorithms but not the command-line scripts rrdesi and rrboss. We keep breaking these scripts but not immediately noticing because the tests don't cover them (e.g. PR #65 completely broke rrdesi due to an incorrect import, and #67 broke some options).

Add unit tests that create spectra and spPlate files on the fly and test that these scripts and their options still work.