$(localstatedir) != $(prefix)/var

$(localstatedir) != $(prefix)/var

The current code assumes that localstatedir is equal to $(prefix)/var,
thus failing for example on debian, where prefix is /usr and
localstatedir is /var. This patch fixes this by expanding LXCPATH just
once in configure.ac to $(localstatedir)/lib/lxc and expanding that
variable everywhere else.

install-exec-local is changed to just do one mkdir -p, and taking into
account of the DESTDIR variable, user for example for packaging.

Changing the permission of LXCPATH is done in lxc-setcap

Signed-off-by: Guido Trotter <ultrotter@quaqua.net>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>