ltp-testsuite: mark as broken

The install step, done with fakeroot, tries to install things in /opt:

make[2]: Entering directory `/home/test/buildroot/output.ctng-arm-eglibc-2010-05-07-19-39-56/target/root/ltp-full-20090630/lib'
install -D -m 644 libltp.a //opt/ltp/lib/libltp.a
install: cannot create directory //opt/ltp: Permission denied
make[2]: *** [install] Error 1

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>