HVDC test timing

[acostarelli]

Haven't investigated why yet, but the HVDC tests seem to take so much longer than any other test suite.

[luke-kiernan]

Yeah this is nothing new. See issue #64.

I recall looking into it and finding that we're running 24+ time steps. I thought I cut that number down to like 3 or 4, but now I don't see that change...