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.

I ran the `clinseq-wer` test on this and it succeeded and produced no diffs.