package/python-bluezero: needs python3

python3 is mandatory since version 0.4.0 and
https://github.com/ukBaz/python-bluezero/commit/55dc0fbc2710a75c9e8f519428e6b10747bf6eb7
https://github.com/ukBaz/python-bluezero/commit/66e1b726d060f3d2b500ba2ec8268cf6743d65e9

Fixes:
 - http://autobuild.buildroot.org/results/cb4d637f1b0ca02377c04d67e20c48784b65c13a



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>