podman machine start: fix ready service

When debugging #17403, the logs of sshd indicates that Podman tried to
ssh into the machine too soon as the `core` user has not yet been fully
set up:

 > error: kex_exchange_identification: Connection closed by remote host
 > fatal: Access denied for user core by PAM account configuration [preauth]

@dustymabe found that the we may have to wait for systemd-user sessions
to be up.  Doing that reduces the flake rate on my M2 machine but does
not entirely fix the issue.

Since I have seen multiple symptoms of flakiness, I think it does not
hurt to add the systemd-user sessions to the dependencies of the ready
service and continue investigating.

[NO NEW TESTS NEEDED] - once we have a fix out, I want to exercise
frequent stop/start in the machine tests but they won't pass now.

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

pkg/machine/hyperv/machine.go

@@ -178,6 +178,7 @@ func (m *HyperVMachine) Init(opts machine.InitOptions) (bool, error) {
 	// VSOCK-CONNECT:2 <- shortcut to connect to the hostvm
 	ready := `[Unit]
 After=remove-moby.service sshd.socket sshd.service
+After=systemd-user-sessions.service
 OnFailure=emergency.target
 OnFailureJobMode=isolate
 [Service]

pkg/machine/qemu/machine.go

@@ -334,6 +334,7 @@ func (v *MachineVM) Init(opts machine.InitOptions) (bool, error) {
 	ready := `[Unit]
 Requires=dev-virtio\\x2dports-%s.device
 After=remove-moby.service sshd.socket sshd.service
+After=systemd-user-sessions.service
 OnFailure=emergency.target
 OnFailureJobMode=isolate
 [Service]