add single reaction deletion unit test
add single reaction deletion unit test

Shorten FVA test by running every other reaction so tests don't take as
long.

jeicher/cobrapy,jerkos/cobrapy,aebrahim/cobrapy,aebrahim/cobrapy,JuBra/cobrapy,jerkos/cobrapy,zakandrewking/cobrapy,zakandrewking/cobrapy,JuBra/cobrapy,jeicher/cobrapy