hard-code bam-readcount version to preserve prior behavior

This is a continuation of #76.  #76 would crash the clinseq-wer test because
the test model set the bam-readcount version to 0.4 but "Produce a report using
DOCM" and "Generate SnvIndel Report" would pass incompatible options to
bam-readcount in that case.  This hard-codes those steps to use bam-readcount
0.6 to get tests back to passing; additional work will need to be done to deal
with this well.