Fix tool_utils.c build when HAVE_SETNS is unset

[pkun]

When HAVE_SETNS is unset the tool_utils.c can't be build because it can't find setns(). The inline setns() is defined in lxc/utils.h but isn't defined in lxc/tools/tool_utils.h. The patch fixes it. Another minor patch fixes headers in lxc/tools to use their own defines to disable double including ( __LXC_TOOLS_UTILS_H).

[lxc-jenkins]

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[brauner]

Thanks for the patch but before I can even look at it you need to sign-off your commits kernel DCO style. Should be as easy as git commit -s.