Register the vm provisioning deadline under a separate label

We have a known issue #718. If the label that we register deadline
fails, we can't persist the deadline information to the strand's stack.
When there is no space left, an exception is raised, preventing the vm
strand from saving the deadline. We don't receive pages due to slow
provisioning if the delay is caused by capacity issues.

I moved the deadline registration to a different label until we find an
elegant solution for issue #718.

prog/vm/nexus.rb

@@ -195,7 +195,10 @@ def before_run
 
   label def start
     register_deadline(:wait, 10 * 60)
+    hop_allocate_vm
+  end
 
+  label def allocate_vm
     vm_host_id = allocate
     vm_host = VmHost[vm_host_id]
     ip4, address = vm_host.ip4_random_vm_network if vm.ip4_enabled

spec/prog/vm/nexus_spec.rb

@@ -225,6 +225,13 @@
   end
 
   describe "#start" do
+    it "registers a deadline and hops" do
+      expect(nx).to receive(:register_deadline)
+      expect { nx.start }.to hop("allocate_vm")
+    end
+  end
+
+  describe "#allocate_vm" do
     it "allocates the vm to a host" do
       vmh_id = "46ca6ded-b056-4723-bd91-612959f52f6f"
       vmh = VmHost.new(
@@ -239,7 +246,7 @@
         expect(args[:vm_host_id]).to match vmh_id
       end
 
-      expect { nx.start }.to hop("create_unix_user")
+      expect { nx.allocate_vm }.to hop("create_unix_user")
     end
 
     it "allocates the vm to a host with IPv4 address" do
@@ -258,7 +265,7 @@
       expect(AssignedVmAddress).to receive(:create_with_id).and_return(assigned_address)
       expect(vm).to receive(:update)
 
-      expect { nx.start }.to hop("create_unix_user")
+      expect { nx.allocate_vm }.to hop("create_unix_user")
     end
 
     it "fails if there is no ip address available but the vm is ip4 enabled" do
@@ -273,7 +280,7 @@
       expect(vmh).to receive(:ip4_random_vm_network).and_return([nil, nil])
       expect(vm).to receive(:ip4_enabled).and_return(true).at_least(:once)
 
-      expect { nx.start }.to raise_error(RuntimeError, /no ip4 addresses left/)
+      expect { nx.allocate_vm }.to raise_error(RuntimeError, /no ip4 addresses left/)
     end
   end