fix #2030: use looks_like_number for number check

fix #2030: use looks_like_number for number check

since numbers can also be in '1.e-10' format, we have to change
how we check for a number

Scalar::Util is already core and we use it in PVE::Tools, so
no new dependecy.

in case of "NaN" or "Infinity" we omit the key/value pair

else we quote like before

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>