Display busy status of LVM2 PVs (#160787)

A Volume Group is active when any of its Logical Volume mappings are
loaded (and enabled) in the Kernel's device-mapper driver.  Therefore
all the Physical Volumes in the VG (must be considered) active too.
This is exactly equivalent to a mounted file system, as the kernel is
actively using the partition.  Mark active LVM2 PVs as busy in GParted.

Don't use statvfs() for determining sector usage of busy LVM2 PVs as it
will fail with "statvfs(VGNAME): No such file or directory".  Instead
always use the LVM2 PV specific method.

Display the status of the LVM2 PV in the Information dialog using one of
the following relevant messages:
    Not active (Not part of any volume group)
    VGNAME not active
    VGNAME active
(The code uses the VGNAME stored in the partition's first mount point,
as displayed in the "Mount Point" column, rather than going back to the
primary source of the information in the LVM2_PV_Info class).

Temporarily prevent GParted from offering to unmount LVM2 PVs until
activating and deactivating Volume Groups is implemented later.

Bug #160787 - lvm support