github: Use microovn waitready (#15167)

CI fails occasionally due to race:
```
+ sudo microovn cluster bootstrap
Error: Post "http://control.socket/core/control": dial unix /var/snap/microovn/common/state/control.socket: connect: no such file or directory
```

MicroOVN added support for a `waitready` subcommand for us in
canonical/microovn#225, we just need to use it.

MicroCeph is [not
affected](https://github.com/canonical/microceph/blob/210e20f30bba4b3e0c9247bdd6539d70f1ccedfb/microceph/cmd/microceph/cluster_bootstrap.go#L80).

Author: tomponline

.github/actions/setup-microovn/action.yml

@@ -25,4 +25,5 @@ runs:
 
           sudo snap install microovn --channel "${{ inputs.microovn-channel }}"
           sudo microovn cluster bootstrap
+          sudo microovn waitready
           sudo microovn status