build: declare lvm_lv_from_name() if it is missing from lvm2app.h

The bd-xlator can not be built successfully on certain Debian
distributions due to a missing declaration of lvm_lv_from_name(). This
function is available for linking, but it does not exist in the header
file.

This change adds a detection for lvm_lv_from_name() in both the library
for linking, and the declaration in the header file. If the 1st is
missing, the bd-xlator can not be built, and if only the 2nd one is
missing, we'll declare lvm_lv_from_name() ourselves. This makes it
possible to build the bd-xlator on the affected Debian distributions
too.

Change-Id: I0c823a7861b02bb5d9c1abb76ebfff92f272f9eb
BUG: 976946
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/5250
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>