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!

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