Improve version handling to prevent inadvertent downgrades

[demonbane]

Added support for actually comparing version numbers rather than just seeing if the new filename is different from the existing one (and fixed a couple of rpm-related bugs that I didn't even know were there). This should help address a possible side-effect of the problem described in #224 -- if you manually ran plexupdate.sh -p while this was happening, but then later went back to PlexPass, you'd get downgraded. That should no longer happen at least.

This should also make it slightly easier to implement support for checking both public and PlexPass at some point in the future and just picking whichever one is newer (just in case this ends up being a recurring problem).

[derekcentrico]

Using your series of commits. No one is streaming and I get an error about connected folks. I mean if people leave an app running in the background and it does some keep alive deal on the connection that kind of kills this whole deal? I can only imagine that's what is going on as no streams are ongoing.

Retrieving list of available distributions
Downloading release "plexmediaserver_1.12.0.4829-6de959918_amd64.deb"
File downloaded
ERROR: Server 127.0.0.1 is currently being used by one or more users, skipping installation. Please run again later

Thoughts?

[demonbane]

@derekcentrico Can you please open a separate issue for this? I'm looking at it right now, I just want to keep the conversation relevant since this PR doesn't touch any of the activity checking code.