Unable to Place Environment Varibles in field resources.workers.sim_workers.nodes of merlin section

[lvandeca]

Bug Report

Describe the bug
In the field resources.workers.<worker_type>.nodes placing environment variables causes an error that the variable is not of type 'null' or does not conform to the format '$(VARNAME)' even when the variable is in the correct format.

To Reproduce
To reproduce the behavior, place any environment variable in the node field of the resources section as shown below:

env:
    variables:
        NODES: 1
merlin:
    resources:
        task_server: celery
        workers:
            simworkers:
                steps: [simulations]
                args: -l ERROR --concurrency 32 --prefetch-multiplier 1 -O fair
                nodes: $(NODES)
                machines: [quartz]

Expected behavior
Merlin should build the DAG, generate any samples, and the value assigned to $(NODES) should be substituted in.

Screenshots
The error that is given when executing merlin run <file>.yaml

[bgunnar5]

This issue is resolved in #484