fs_util exits 2 for ENOENT (#5064)
fs_util exits 2 for ENOENT (#5064)

This allows tools using it to differentiate error causes.
UnrememberMe/pants,UnrememberMe/pants,pantsbuild/pants,jsirois/pants,foursquare/pants,fkorotkov/pants,UnrememberMe/pants,fkorotkov/pants,tdyas/pants,benjyw/pants,tdyas/pants,wisechengyi/pants,wisechengyi/pants,wisechengyi/pants,UnrememberMe/pants,baroquebobcat/pants,foursquare/pants,fkorotkov/pants,jsirois/pants,baroquebobcat/pants,benjyw/pants,tdyas/pants,wisechengyi/pants,fkorotkov/pants,UnrememberMe/pants,foursquare/pants,twitter/pants,twitter/pants,pantsbuild/pants,benjyw/pants,fkorotkov/pants,tdyas/pants,pantsbuild/pants,wisechengyi/pants,fkorotkov/pants,baroquebobcat/pants,tdyas/pants,fkorotkov/pants,benjyw/pants,twitter/pants,jsirois/pants,wisechengyi/pants,foursquare/pants,baroquebobcat/pants,tdyas/pants,twitter/pants,twitter/pants,foursquare/pants,tdyas/pants,baroquebobcat/pants,twitter/pants,UnrememberMe/pants,twitter/pants,baroquebobcat/pants,wisechengyi/pants,tdyas/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,wisechengyi/pants,foursquare/pants,foursquare/pants,fkorotkov/pants,baroquebobcat/pants,twitter/pants,foursquare/pants,pantsbuild/pants,baroquebobcat/pants,foursquare/pants,UnrememberMe/pants,baroquebobcat/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,twitter/pants,UnrememberMe/pants,wisechengyi/pants,tdyas/pants,UnrememberMe/pants