Turbostat plugin: relax dependency on root

Turbostat plugin: relax dependency on root

Backporting commit 98481e79b60a50d699b79292ff1b7e56e7fa8425
from Len Brown <len.brown@intel.com>

For turbostat to run as non-root, it needs to permissions:

1. read access to /dev/cpu/*/msr
        via standard user/group/world file permissions

2. CAP_SYS_RAWIO
        eg.  # setcap cap_sys_rawio=ep $(which collectd)

Yes, running as root still works.