tests: Rename usb-controller-implicit-*

tests: Rename usb-controller-implicit-*

To usb-controller-automatic-*.

This matches the existing q35 test, and in general makes more
sense as a name since these tests are providing coverage for
USB controllers getting automatically added by libvirt for new
domains, rather than implicit (i.e. built-in, non-removable)
devices.

Note that, in the case of physical i440fx machines, the USB
controller is actually part of the chipset and would thus
qualify as implicit; the corresponding QEMU machine type,
however, allows for it to be removed, so the new name is still
more appropriate when discussing virtual hardware.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>