Need longer timeout and retries when probing instance for mount support

When an instance is finished booting, it's possible it's very busy starting and running services. As such, when `multipassd` probes the instance to determine if mount support is enabled, etc., the instance may be so busy that the probing may time out. We should increase the timeout and/or add some retries.

---
_Original message:_
I am still having this issue with
```
multipass 1.12.2
multipassd 1.12.2
```
[mp.log](https://github.com/canonical/multipass/files/12654425/mp.log)

_Originally posted by @sed-i in https://github.com/canonical/multipass/issues/2986#issuecomment-1724664169_