support not-MAC-address based UUID versions

So far as I know, this affects all versions of MariaDB.

On Linux, FreeBSD, and (perhaps) MacOS, MariaDB uses the host MAC address as the basis for generating v1 UUID values in the UUID() function. On Windows, it generates a random nonce and uses that instead of a MAC address.

In cloud or virtual machine deployments, it is likely that

1. MAC addresses are not unique (e.g. all Hyper-V installations use the same small pool by default), or
2. Multiple copies of MariaDB may end up running in adjacent containers that execute on the same underlying machine (and therefore share a MAC address).

On Windows deployments this has not been an issue, because these deployments generate random nonces instead of using the MAC address.

It would be helpful if it were possible to configure the Linux/FreeBSD/?Mac installations to use such a nonce in environments where the uniqueness of the MAC address is uncertain or unreliable. Since the nonce support code is already present, one might hope this would not be a big lift.