CRUNCH-696 update FormatBundle.readFields() compatibility

Make FormatBundle.readFields() compatible with FormatBundles serialized
with an older version of Crunch.  This ensures jobs don't fail during an
upgrade to a cluster-provided Crunch dependency.  Without this some jobs
get submitted without the filesystem field in the serialized
FormatBundle and then encounter EOFException when the job gets
scheduled to run and uses the newer Crunch to deserialize the FormatBundle.
1 file changed