cap profiling period by 10 minutes
cap profiling period by 10 minutes

See https://github.com/NebulousLabs/Sia/pull/1806#issuecomment-303827861

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