Add lvm2app interfaces to lookup a vgname from a pvid and pvname.

Add lvm2app interfaces to lookup a vgname from a pvid and pvname.

lvm2app forces applications to start with a volume group name,
open the volume group, then operate on individual pvs.  In some
cases the application may want to start with a device name rather
than the volume group name.  Today, if an application wants to
do this, it must iterate through all the volume groups to find
the volume group that the specific device is attached to.
These new interfaces allow the application to avoid such overhead.
Bump the lvm2app version number to 3.