virt-install: Turn --os-type into a no op and warning

I'm still seeing blog posts that recommend using

  --os-type linux --os-variant XXX

Which has been a no op for a long time but is mostly harmless.
Current git would make this an error condition, but that's too
disruptive IMO. Just print a warning

Signed-off-by: Cole Robinson <crobinso@redhat.com>

tests/test_cli.py

@@ -943,7 +943,7 @@ c.add_invalid("--paravirt --import --print-xml 2")  # PV Import install, no seco
 c.add_invalid("--paravirt --import --print-xml 7")  # Invalid --print-xml arg
 c.add_invalid("--location kernel=foo,initrd=bar")  # location kernel/initrd without any url
 c.add_invalid("--location http://example.com,kernel=foo")  # location without kernel+initrd specified as pair
-c.add_invalid("--os-type linux", grep="Unknown OS name 'linux'")
+c.add_valid("--pxe --os-type linux", grep="--os-type is deprecated")
 c.add_invalid("--os-variant solaris10 --unattended", grep="not support unattended")
 
 c = vinst.add_category("misc-install", "--nographics --noautoconsole")

virtinst/virtinstall.py

@@ -143,8 +143,10 @@ def convert_old_disks(options):
 
 
 def convert_old_os_options(options):
-    if not options.os_variant and options.old_os_type:
-        options.os_variant = options.old_os_type
+    if not options.old_os_type:
+        return
+    log.warning(
+        _("--os-type is deprecated and does nothing. Please stop using it."))
     del(options.old_os_type)