autoconf: use $(LIBOSD) $(LIBCOMMON) instead of libosd.a libcommon.la

hardcoded library names in unit test dependencies break compilation

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #581 from dachary/master

autoconf: use $(LIBOSD) $(LIBCOMMON) instead of libosd.a libcommon.la

Reviewed-by: Sage Weil <sage@inktank.com>