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.

 `issym` checks for exact match
https://github.com/JuliaLang/julia/blob/master/base/sparse/sparsematrix.jl#L1899

SCS.jl enforces symmetricity through explicit equality constraints, so we're likely going to have precision issues.

I don't think the following would be a problem here, but it's another place where I ran into issues with `issym`:
```
A = [0.8608 0.3131 0.5458; 0.3131 0.8584 0.5836; 0.5458 0.5836 1.5422];
issym(A)
true
issym(A'*A*A*A')
false
```