SSDs not HDDs

[dpmccabe]

No change to any WDL except using SSDs instead of HDDs everywhere inside the RNA_pipeline and WGS_pipeline folders:

• Hard-coded "HDD" in our WDL is now "SSD".
• WDL imported from Github where a use_ssd option was already available as a task input now uses use_ssd = true whenever such a task is called.
• WDL imported from Github where HDDs are hard-coded have been forked into this gist where the only changes are fixing that thing.