test-seccomp: check for CAP_IPC_OWNER before calling shmat()
shmat() requires the CAP_IPC_OWNER capability. When running test-seccomp
in environments with root + CAP_SYS_ADMIN, but not CAP_IPC_OWNER,
memory_deny_write_execute_shmat would fail. This fixes it.
(cherry picked from commit 7e46a5c093e9e0d2e1ec734058e0caf1725ff37e)