NEOS Connection and Message Updates

[mrmundt]

Fixes NA

Summary/Motivation:

We made some changes in #3644 that we weren't hugely a fan of w.r.t. the NEOS connection exceptions. This makes that more robust as well as updating the printout for pyomo solvers --help to provide the user with more information about why NEOS doesn't work, assuming it fails.

Changes proposed in this PR:

• More robust connection checking
• Minor other updates to NEOS interface
• Updates to NEOS availability statement
• Tests!

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.