Change the install directory for the tools

Currently, the tools are installed under $prefix/share/ganeti. This
prevents installing other things in a nice way under share/ganeti (like
arch-independent OS definitions), therefore we want the tools to live
under share/ganeti/tools.

A second change is that since these are programs, they would better live
under libdir than datadir - we might have to change them later to
binaries in which case 'share' is definitely not the way to go.

This patch therefore changes the install directory for the tools to
$prefix/lib/ganeti/tools.

Reviewed-by: imsnah