Speeding up minor variants analysis

[vrennie]

@mdediegofuertes noticed a long run time related to this. Could be worth to use a threading tag to increase parallelisation

[abhi18av]

Expanding on the context here

• Threading tag from tb-profiler
• Also worth investigating whether the problem happens only with processes in structural variant analysis

[abhi18av]

I discussed this part with @jodyphelan as part of a general optimizations which could be made in `tb-profiler.