Better communication around LOGIN command

[gbakeman]

According to the NUT protocol manual, the LOGIN command is only necessary to coordinate with the UPS when shutting down essential devices. From some other testing, I've found that it isn't necessary to LOGIN in order to read UPS data, which is what we do most of the time anyways. In fact, the manual notes that logging in should only be used in specific circumstances.

WinNUT's connection routine and preferences should be modified such that logging in is only done when explicitly requested by the user, otherwise only the LOGOUT command will be used when disconnecting gracefully.

In addition, it's apparent that different distributions of NUT behave differently with regards to the LOGIN command, sometimes not even supporting it entirely. This needs to be communicated with the user more effectively. Some examples of LOGIN command issues:

• FormatException in GetPowerUsage causes repeated disconnects #123

Related

• Prefs_Gui upgrade #102
• Resuming from Sleep and other connection fixes #163