raise an error if more than 20% of the reads get assigned to Undetermined

[antgonza]

bcl-convert log outlines the total reads and how many were Undetermined:

Lane 4 Post-run Information:
Total clusters: 3768318494
Total Genomic Reads: 7536636988
Total Genomic Input Gigabases 1138.03
Minimum reads for a sample: 0
Maximum reads for a sample: 106
Average reads per sample: 0.51
Undetermined reads: 7536636792