Make ENV variables for the experiment parameters

[emil916]

Gabe mentioned here:
"I'm guessing these can be overridden by env variables?"

Originally posted by @gparmer in #257 (comment)

Sean's suggestion:
Not the way it's written currently, but something like local -ir worker_max=${WORKER_MAX:-50} would do with trick with a default value if it's not defined. Likely a better approach than noise diffs!

Lines:

sledge-serverless-framework/runtime/experiments/workload_mix_realworld/run.sh

Lines 105 to 110 in 7640cd5

	local -ir batch_size=1
	local -i batch_id=0
	local -i roll=0
	local -ir total_iterations=10000
	local -ir worker_max=50
	local pids