[LibOS] test/apps: Skip meaningless signal06 test in LTP
The LTP test signal06 is a regression test for some obscure bug in older
Linux kernels. It uses SIGHUP and SIGSEGV signals to test mprotect() of
altstack. Since SIGHUP is completely ignored by Graphene, and altstack is
not correctly emulated, and mprotect() doesn't work, this test never made
sense for Graphene. This commit disables it.
Dmitrii Kuvaiskii