Make `--domainname` undocumented

UTS related options are probably not worth positions in help text.
Just make `--hostname` visible and keep other 4 undocumented.
Rakefile: make ruby 1.8 happy

Why Ubuntu 14.04 still ships the acient ruby ... I don't understand
Remove debug code

It actually could be a serious security issue.
Drop libseccomp1 support

We need seccomp_syscall_resolve_name and seccomp_rule_add_array.
Fix compiler warnings
Add integration test about syscall filters
Bump to 0.9.9

Remove version related stuff in README to make it clean