cpu-gather: Move msr decoding to new script

cpu-gather: Move msr decoding to new script

Fixes the leaking file descriptors. Does not silently ignore errors
(e.g. permission denied on /dev/cpu/0/msr if run as non-root) and
always attempt to read from /dev/kvm if /dev/cpu/0/msr failed.

'gather_msr()' returns a dictionary of values, as a later patch will
add more registers to be interrogated.

Signed-off-by: Tim Wiederhake <twiederh@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>