osdict: Fix incorrect usage of virtio input

Regression reported with latest libosinfo, when the OS reports
virtio-input support:

http://www.redhat.com/archives/virt-tools-list/2016-July/msg00109.html

Really our code presently only cares about the USB tablet, so adjust
our libosinfo lookup to explicitly check for it

virtinst/guest.py

@@ -1031,15 +1031,14 @@ class Guest(XMLBuilder):
                 return False
             return all([c.model == "none" for c in controllers])
 
-        input_type = self._os_object.default_inputtype()
-        input_bus = self._os_object.default_inputbus()
+        input_type = "mouse"
+        input_bus = "ps2"
         if self.os.is_xenpv():
             input_type = VirtualInputDevice.TYPE_MOUSE
             input_bus = VirtualInputDevice.BUS_XEN
-        elif _usb_disabled() and input_bus == "usb":
-            input_bus = "ps2"
-            if input_type == "tablet":
-                input_type = "mouse"
+        elif self._os_object.supports_usbtablet() and not _usb_disabled():
+            input_type = "tablet"
+            input_bus = "usb"
 
         for inp in self.get_devices("input"):
             if (inp.type == inp.TYPE_DEFAULT and

virtinst/osdict.py

@@ -457,23 +457,19 @@ class _OsVariant(object):
                 return devname
         return None
 
-    def default_inputtype(self):
-        if self._os:
-            fltr = libosinfo.Filter()
-            fltr.add_constraint("class", "input")
-            devs = self._os.get_all_devices(fltr)
-            if devs.get_length():
-                return devs.get_nth(0).get_name()
-        return "mouse"
+    def supports_usbtablet(self):
+        if not self._os:
+            return False
 
-    def default_inputbus(self):
-        if self._os:
-            fltr = libosinfo.Filter()
-            fltr.add_constraint("class", "input")
-            devs = self._os.get_all_devices(fltr)
-            if devs.get_length():
-                return devs.get_nth(0).get_bus_type()
-        return "ps2"
+        fltr = libosinfo.Filter()
+        fltr.add_constraint("class", "input")
+        fltr.add_constraint("name", "tablet")
+        devs = self._os.get_all_devices(fltr)
+        for idx in range(devs.get_length()):
+            dev = devs.get_nth(idx)
+            if devs.get_nth(idx).get_bus_type() == "usb":
+                return True
+        return False
 
     def supports_virtiodisk(self):
         if self._os: