plot_vaf:calculate_adjVAF_Python fails with multiple tumor sample input

[sorelfitzgibbon]

When run in multi-sample mode, the pipeline assigns sample-id = patient-id. I think plot_vaf is looking for the actual sample id within the VCF and fails. Either skip plot_vaf for multiiple or update to plot VAF for each sample (always only mutect2 for multiple samples).

[yashpatel6]

Plot-vaf should probably be skipped for the multi-sample case; the plot is intended to compare between variants based on consensus and we only run Mutect2 in multi-mode so the plot wouldn't really show much