Creating node sometimes segfaults in linux

[osrf-migration]

Original report (archived issue) by Poh Zhi-Ee (Bitbucket: Poh Zhi-Ee).

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This is due to the lack of error handling for the getpwuid_r() call in the username() function in NetUtils.cc
According to the getpwuid_r manpage the function is not always successful. Failing to handle the errors but continuing to use the passwd struct can result in the use of a corrupted data structure which causes a segfault.

Additional information:
Stack trace of the segfault

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