Fix octoprint versioning by checking python version

[umberd]

Hello,

The goal of this pull request is to consider that people could have different versions of python3 depend on their firmware.

So I made an adjustment to check which version of Octoprint people will have to install.

This should theoretically fix #42 #43 #46 #47 #50

[umberd]

I made this patch without having an owrt os under my hands. Please consider to review my work on a working card with openwrt inside