Improve data not found error messages.

[kevinwheeler]

If the data directory or file is not found, output the exception message. If it was the directory that wasn't found, prompt the user to consider using Globals.DataFolder to make sure they are using the correct data folder if running in a docker container.

Description

Related Issue

N/A

Motivation and Context

I needed the improved error message to figure out why my data directory/files kept not being found. Since I made the changes anyways, I thought I might as well push them.

Requires Documentation Change

No

How Has This Been Tested?

I ran "lean build" and then used this custom image when using the lean cli to run a backtest with the wrong data directory. The error message was properly included.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Refactor (non-breaking change which improves implementation)
• Performance (non-breaking change which improves performance. Please add associated performance test and results)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• [ X] Non-functional change (xml comments/documentation/etc)

Checklist:

• [ X] My code follows the code style of this project.
• [ X] I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
  Not sure how I would test this. The error message isn't returned by the function where it is generated. It gets incorporated into a new object that is created.
• [ X] All new and existing tests passed.
• My branch follows the naming convention bug-<issue#>-<description> or feature-<issue#>-<description>

[Martin-Molinero]

Thank you @kevinwheeler! Welcome to Lean ✨