don't try to build cgm-concurrent test when doing make dist

making the whole tests dir an EXTRA_DIST means that make will try to
build it even when just doing a make dist which fails if you don't
already have cgmanger installed. Probably tests should be
made DIST_SUBDIRS and SUBDIRS but I was having trouble adding the
right dependency to ensure the library was built before the test.

also remove libnih-dbus from .spec since it is provided by libnih pkg

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>