osdict: Make qemu_ga support solely dependent on virtio-serial support

We shouldn't concern ourselves with whether the OS supports qemu_ga
out of the box, just set up the channel regardless, as long as
virtio-serial is supported.

This adds the channel for some aarch64 cases which didn't have OS
specified, but that's desired IMO

tests/cli-test-xml/compare/virt-install-aarch64-cdrom.xml

@@ -36,6 +36,10 @@
       <model type="virtio"/>
     </interface>
     <console type="pty"/>
+    <channel type="unix">
+      <source mode="bind"/>
+      <target type="virtio" name="org.qemu.guest_agent.0"/>
+    </channel>
   </devices>
 </domain>
 <domain type="qemu">
@@ -73,5 +77,9 @@
       <model type="virtio"/>
     </interface>
     <console type="pty"/>
+    <channel type="unix">
+      <source mode="bind"/>
+      <target type="virtio" name="org.qemu.guest_agent.0"/>
+    </channel>
   </devices>
 </domain>

tests/cli-test-xml/compare/virt-install-aarch64-machdefault.xml

@@ -29,5 +29,9 @@
       <model type="virtio"/>
     </interface>
     <console type="pty"/>
+    <channel type="unix">
+      <source mode="bind"/>
+      <target type="virtio" name="org.qemu.guest_agent.0"/>
+    </channel>
   </devices>
 </domain>

tests/cli-test-xml/compare/virt-install-aarch64-machvirt.xml

@@ -29,5 +29,9 @@
       <model type="virtio"/>
     </interface>
     <console type="pty"/>
+    <channel type="unix">
+      <source mode="bind"/>
+      <target type="virtio" name="org.qemu.guest_agent.0"/>
+    </channel>
   </devices>
 </domain>

virtinst/guest.py

@@ -659,7 +659,7 @@ class Guest(XMLBuilder):
             return
 
         if (self.conn.is_qemu() and
-            self._os_object.supports_qemu_ga() and
+            self._supports_virtio(self._os_object.supports_virtioserial()) and
             self.conn.check_support(self.conn.SUPPORT_CONN_AUTOSOCKET)):
             dev = DeviceChannel(self.conn)
             dev.type = "unix"

virtinst/osdict.py

@@ -336,10 +336,6 @@ class _OsVariant(object):
             return "localtime"
         return "utc"
 
-    def supports_qemu_ga(self):
-        return self._is_related_to(
-                ["debian8", "fedora18", "rhel6.0", "sles11sp4"])
-
     def supported_netmodels(self):
         return self._device_filter(cls="net")
 
@@ -355,6 +351,12 @@ class _OsVariant(object):
     def supports_virtiorng(self):
         return bool(self._device_filter(cls="rng", name="virtio.*-rng"))
 
+    def supports_virtioserial(self):
+        if self._device_filter(cls="console", name="virtio.*-console"):
+            return True
+        # 2018-09-01: osinfo data is wrong for RHEL/centos here
+        return self._is_related_to("rhel6.0")
+
     def get_recommended_resources(self, guest):
         ret = {}
         if not self._os: