Shared VPC support is blocked by firewall rule

[mdhedley]

The use of shared VPC appears to be supported but fails when it attempts to create the firewall based on the network name.

Example: datalab create --network-name /projects//global/networks/ --subnet

Produces error: Creating the firewall rule projects//global/networks/-allow-ssh

Creating firewall... failed. ERROR: (gcloud.compute.firewall-rules.create) Could not fetch resource:

• Invalid value for field 'resource.name': 'projects//global/networks/-allow-ssh'. Must be a match of regex '(?:a-z?)'

This prevents the use of shared vpcs with datalab.