Make lvm2 plugin lvmdump option collect metadata

The lvmdump-a option currently collects 'advanced' data but not
raw metadata. Since it's off by default and the metadata is often
of interest in support cases rename the option to lvmdump-am and
have it also pass the '-m' (raw metadata) option to the lvmdump
script.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>