Explicit mode now available in launch_experiment script

[arik-shurygin]

users are now able to point to a csv containing task parameters to launch an arbitrary number and layout of tasks with launch_experiment

example
the user wants to run the following tasks, each with the following run_task.py calls

python run_task.py --jobid example-jobid-1 --state CA --scenario example-scenario1
python run_task.py --jobid example-jobid-1 --state CA --scenario example-scenario2
python run_task.py --jobid example-jobid-1 --state CA --scenario example-scenario3
python run_task.py --jobid example-jobid-1 --state OR --scenario example-scenario1
python run_task.py --jobid example-jobid-1 --state OR --scenario example-scenario2
python run_task.py --jobid example-jobid-1 --state OR --scenario example-scenario3

In short, they want to run 3 scenarios across 2 states.
their explicit_mode.csv file would look like

state,scenario
CA,example-scenario1
CA,example-scenario2
CA,example-scenario3
OR,example-scenario1
OR,example-scenario2
OR,example-scenario3

and their call to launch_experiment would look like:
launch_experiment --job_id example-jobid-1 -e example_experiment --explicit path/to/explicit_mode.csv