Refactor svirt backend (vmware specific functions in backend/svirt.pm, consoles/sshVirtsh.pm)
svirt backend got support for many targets, so it needs refactoring.
One thing what needs to be done is using vmware specific functions in backend/svirt.pm and consoles/sshVirtsh.pm (use of VMWARE_REMOTE_VMM variable).
add_disk() in consoles/sshVirtsh.pm is too long, also uses VMWARE_REMOTE_VMM in non-vmware context, which is confusing.
Fixes like https://github.com/os-autoinst/os-autoinst/pull/1099 are just remove warnings, which point to the problem.