add docstrings to new renter test functions
add docstrings to new renter test functions

ChrisSchinnerl/Sia,mharkus/Sia,MrStrong/Sia,rivine/rivine,mtlynch/Sia,ericflo/Sia,ChrisSchinnerl/Sia,rivine/rivine,NebulousLabs/Sia,ericflo/Sia,mtlynch/Sia,NebulousLabs/Sia,MrStrong/Sia,mharkus/Sia,mnsl/Sia,mnsl/Sia