sometimes EOS versions can contain a sub patch version

[dathelen]

My customer has a bunch of 7050QX switches that have shipped with the following eos version:

4.14.5FX.2

This causes issues for the follow code in the bootstrap client file:
https://github.com/arista-eosplus/ztpserver/blob/develop/client/bootstrap#L437

as there are now 4 values to unpack.

I think changing that line to:

(major, minor, patch) = version.split('.')[0:3]

seems to do the trick and keeps the needed functionality since the sub patch version wont be a determining factor if unix sockets are available