Shallow water HLLE solver tests

[ketch]

This PR provides tests for the solvers add in clawpack/riemann#145.

[coveralls]

Coverage remained the same at ?% when pulling 3df2ffc on ketch:sw_hlle into f396ebc on clawpack:master.

[coveralls]

Coverage remained the same at ?% when pulling d71832b on ketch:sw_hlle into f396ebc on clawpack:master.

[mandli]

I forgot we need to update clawpack/clawpack with the Riemann solver. I can do a quick update to clawpack/clawpack as long as it does not disrupt the testing of clawpack/clawpack#141.

[mandli]

PetClaw is failing and I am not sure why. This all works for me but there may be something that's built differently as usual.

[ketch]

I wrote the tests incorrectly; in PetClaw, get_q_global() gives the solution on process 0 but gives None on other processes. I've fixed it now.