Update for Dbvis Connections Settings Module

This pull request includes the following changes:

* Retabbed and reformatted
* Made checks more specific (ie: EOFError handling, file path)
* Module name change
* Using Rex to check IPv4 format instead of using resolv
* Other corrections

@philophobia78 Please test this PR. After you land this, your pull request at https://github.com/rapid7/metasploit-framework/pull/3522 will be updated automatically.