ensure WDL compatibility with Azure

[vsmalladi]

See compatibility notes here:
https://github.com/microsoft/CromwellOnAzure/blob/master/docs/change-existing-WDL-for-Azure.md/#How-to-modify-an-existing-WDL-file-to-run-on-Cromwell-on-Azure

Mostly focused on making sure some of the runtime block items are specified in compatible ways (ie, that memory and disk always have units attached) and that we add a maxRetries synonym for wherever we specify preemptible. We might already be compatible, it's just worth going through and double checking...

[kapsakcj]

Thanks for letting us know and for the information! This will be a necessary change as Terra on Azure becomes available.

[vsmalladi]

Will try to do a pr next week to get this started