This commit share host Real Time Clock device (rtc) into LXC containers
to support hardware clock. This should be available setting up a `rtc`
timer under clock section. Since this option is not emulated, it should
be available only for `localtime` clock. This option should be readonly
due to security reasons.

Before:
    root# hwclock --verbose
    hwclock from util-linux 2.32.1
    System Time: 1581877557.598365
    Trying to open: /dev/rtc0
    Trying to open: /dev/rtc
    Trying to open: /dev/misc/rtc
    No usable clock interface found.
    hwclock: Cannot access the Hardware Clock via any known method.

Now:
    root# hwclock
    2020-02-16 18:23:55.374134+00:00
    root# hwclock -w
    hwclock: ioctl(RTC_SET_TIME) to /dev/rtc to set the time failed:
    Permission denied
Signed-off-by: NJulio Faracco <jcfaracco@gmail.com>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>