Currently we use the HTS_USE_VNC constant only to copy the vnc password
file. While KVM uses vnc it currently has no password support, nor we'll
be on time making one for 2.0, so renaming the constant to
HTS_COPY_VNC_PASSWORD and only putting Xen HVM in it. In the future
(2.1) password handling will need to be reworked anyway.

Reviewed-by: iustinp