Flow status flagged as completed when the conda command fails

[taxe10]

As discussed with @Wiebke. There are some instances where the conda flows do not log execution errors correctly. I think run_conda.sh may be missing something like:

if [ "$?" -ne 0 ]; then
    echo "Failed to run conda command"
    exit 1
fi

echo "Successfully run conda command"
exit 0

Additionally, the conda_flow.py would need:

from prefect.states import Failed
...
if process.returncode != 0:
        return Failed(message="Conda command failed")

@dylanmcreynolds

[taxe10]

Fixed #19