Add bam_readcount_version to somatic_variation

The 'Create Reports' step in somatic variation recently fell victim to the default version change of bam readcount. Somatic variation builds are now using version 0.6 instead of 0.5, without any profile change.

Before this is pushed, I will backfill processing profiles. This will involve some complication as some builds have run on 0.5 and some on 0.6.
Can we make this non-optional.  I understand it is optional in the command we use in execute, but we can be more strict I think.