Updated to use simulation time and gridappsd-python command

[Jeffrey-Simpson]

Updated to use simulation time and gridappsd-python command

Note that the container has to be rebuilt from the base gridappsd container for this to work.

I test by doing this:

docker exec -it gridappsd-docker_pyvvo_1 bash

apt update
apt-get update && apt-get install -y procps
apt install -y git
pip install --upgrade git+git://github.com/GRIDAPPSD/gridappsd-python@releases/2021.02.0


python
from gridappsd import GridAPPSD, topics, simulation
from gridappsd.difference_builder import DifferenceBuilder as DiffBuilder
from gridappsd import utils as gad_utils
# gad_utils.get_gridappsd_user()
diff_builder = DiffBuilder(simulation_id=1234)
diff_builder.get_message(epoch=1)

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This change is