Scaling on summit using:

OS: /ccs/home/zingale/Microphysics/EOS/helmholtz
NETWORK: /ccs/home/zingale/Microphysics/networks/iso7
CONDUCTIVITY: /ccs/home/zingale/Microphysics/conductivity/stellar

Castro       git describe: 20.03-97-g4daf8bcd1
AMReX        git describe: 20.03-149-g7fc56fea8
Microphysics git describe: 20.03-12-g0b4bfbb3

This used the inputs as is (with amr.max_level = 1)

Problem size: 768x768x192
# GPUs      avg_time        std
  192    237.196           25.3064
  384       6.30901         0.17731
  768       3.65006         0.0840747
 1536       2.35438         0.119527


Notice that the lowest GPU count is very slow -- we are
oversubscribing the GPU memory here and paying the penalty.  All of
the larger GPU counts appear to scale very well.

