Add support for Azure low-priority VMs

[pditommaso]

This PR adds initial support for Azure Low-priority VMs by adding a new lowPriority boolean option to the azure pool settings

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[pditommaso]

@adamrtalbot should be ok now

[adamrtalbot]

Just had a go with the following and I span up a low-priority set pool. Thanks @pditommaso!

workDir = "$AZURE_BATCH_WORK_DIR"

process {
    executor = 'azurebatch'

}

azure {
    storage {
        accountName   = "$AZURE_STORAGE_ACCOUNT_NAME"
        accountKey    = "$AZURE_STORAGE_ACCOUNT_KEY"
    }
    batch {
        location      = "$AZURE_BATCH_ACCOUNT_REGION"
        accountName   = "$AZURE_BATCH_ACCOUNT_NAME"
        accountKey    = "$AZURE_BATCH_ACCOUNT_KEY"
        autoPoolMode  = true
        pools {
            auto {
                vmType      = 'Standard_E2d_v4'
                lowPriority = true
            }
        }
    }
}

Command:

nextflow-dev run hello

Result:

[adamrtalbot]

And an autopool version:

workDir = "$AZURE_BATCH_WORK_DIR"

process {
    executor = 'azurebatch'

}

azure {
    storage {
        accountName   = "$AZURE_STORAGE_ACCOUNT_NAME"
        accountKey    = "$AZURE_STORAGE_ACCOUNT_KEY"
    }
    batch {
        location      = "$AZURE_BATCH_ACCOUNT_REGION"
        accountName   = "$AZURE_BATCH_ACCOUNT_NAME"
        accountKey    = "$AZURE_BATCH_ACCOUNT_KEY"
        autoPoolMode  = true
        pools {
            auto {
                vmType      = 'Standard_E2d_v4'
                lowPriority = true
                autoScale = true
            }
        }
    }
}

[pditommaso]

Nice, let's merge

[abhi18av]

Great work guys - I believe this one is definitely worth having in the LTS version!

We can make use of the Low priority VMs as part of Azure megatests on the nf-core side.

[pditommaso]

We can give it a try