iterate_file_lines() 

Add iterate_file_lines() to Genome::Sys.  This method is an abstraction to work through a file one line at a time.

Convert Genome::Model::Build::Command::DetermineError to use it.

There are probably other places it could be used.
I don't think the `ERROR_FINDING_REGEX` can include the regular expression this backwards search is trying to find.  If it did we would have found something in the forward iteration over this file and never reached this subroutine.