util-linux: convert to autotarget and bump to 2.19.1

[Peter: fix deps, restructure, add unshare]
Signed-off-by: Chih-Min Chao <cmchao@gmail.com>
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>