rostest: add missing dependency on python-nose

| CMake Warning at /build/v2012.12/build/tmp-angstrom_v2012_12-eglibc/sysroots/x86_64-linux/usr/share/catkin/cmake/test/nosetests.cmake:90 (message):
|   nosetests not found, Python tests can not be run (try installing package
|   'python-nose')

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>