Better pmm-distribution detection for clouds

Currently, we use ansible_virtualization_type to distinguish between AMI, OVF, and Docker. We check the value of that variable during build to write to /srv/pmm-distribution file:

• if ansible_virtualization_type is "virtualbox", it is OVF;

• if ansible_virtualization_type is "docker", it is Docker;

• if ansible_virtualization_type is "xen" or "kvm" (as AWS moves from Xen to KVM), it is AMI.

That check is incorrect for other clouds like Google Cloud, etc.