Mongod fails to start as unprivileged user when {{/sys/devices/system/node}} is not readable and executable.

Follow-on to SERVER-10623, which we apparently didn't completely resolve.

I'm still having a related issue to this in 2.5.4. Also running on an OVH kernel that /sys/devices/system/node is not readable/executable. On startup, the fatal message is logged:

exception in initAndListen std::exception: boost::filesystem::status:

Permission denied: "/sys/devices/system/node/node1", terminating

While the fix solved processinfo_linux2.cpp's reading of /sys/devices/system/node/node1, there's another attempt to read it inside of startup_warnings.cpp that isn't wrapped with a try/catch.

The function boost::filesystem::exists(boost::filesystem::path) throws an exception if some component of the path is not accessible by the executing user.