VM: Avoid QEMU device ID trimming

[hamistao]

This fixes the duplicate ID problem on qemu when adding a div drive device.
The problem occurs because QEMU trimms down long device IDs to 64 characters internally and that may result in other references to that device mismatching the device ID or even duplicate IDs if a dir drive device ID is big enough that the suffix that differentiates the tags of the 9p entry and the virtiofs entry are removed in the trimming process.
As an example, dev-lxd_{long_device_name}-virtio-fs and dev-lxd_{long_device_name}-9p would be used in separate qem.conf entries for the same device named {long_device_name}. This can generate duplicate IDs when both those ids get trimmed down to dev-lxd_{trimmed_long_device_name}, losing the protocol suffixes.
This PR proposes hashing the device name when the device name is big enough that the QEMU ID has to be trimmed (but not in any other case). This results is device IDs like dev-lxd_{device_name_hash}-virtio-fs

[hamistao]

@tomponline warning that this hashes the device names even if the protocol suffixes would just be partially trimmed, like in dev-lxd_{long_device_name}-v and dev-lxd_long_device_name}-9, so this could change the behavior of devices with very specific name lengths.

[hamistao]

@tomponline this is ready again

[hamistao]

@tomponline I couldn't test this with hotplugging because of the issue you are working on, it may be necessary to use generateQemuDirDriveName when hotplugging a device but I would like to test it before making that decision.

[tomponline]

@tomponline I couldn't test this with hotplugging because of the issue you are working on, it may be necessary to use generateQemuDirDriveName when hotplugging a device but I would like to test it before making that decision.

Yep, we'll land the other hotplug fix first. Good idea.