Update AzureUri for onprem support and handle VssResourceNotFound error

[dkbennett]

Summary of the pull request

Updates AzureUri to handle the format for On-Premeses DevOps servers (aka "onprem").

Also adds a specific error handling message for VssResourceNotFound error, which is what happens if you call an API that the devops server does not support. This was found against a DevOps Express install, which does not appear to have full rest API functionality.

References and relevant issues

Closes #45

Detailed description of the pull request / Additional comments

• Updated AzureUri to support onprem format URIs.
• Updated some error handling to check for the VssResourceNotFound exception.
• Added some error handling strings that were missing which were hit while working on this feature.
• Better handling of the null case of connections, which I encountered when testing onprem.
• Updated the Validation tests for AzureUri to validate on-prem style Uris.
• Updated RepositoryProvider uri validation test to account for the now less-rigid valid formats.

Validation steps performed

• Installed DevOps express, created on-prem server local to my machine and tested the code against URLs to my local devops server.
• Verified new onprem validation tests pass and process as expected.
• Verified repositoryprovider Uri testing passes as before.

PR checklist

• Closes #xxx
• Tests added/passed
• Documentation updated

[EricJohnson327]

Please add comments for all these strings.