add tests for exp primal and sdps

I also added `tol` as an argument since SCS by default isn't accurate enough to 6 decimal digits.

SCS's behavior here is pretty strange. What does it mean to have a nonsymmetric solution to an SDP? Why are there explicit copies of variables when you could just maintain the lower (or upper) triangle internally and avoid nonsymmetry by design?
@madeleineudell