api/admin: exclude regex attribute from DeviceInfo structure

DeviceInfo may contain 'regex' attribute - it isn't intended to be
reported through Admin API. Also, mark 'libvirt_regex' attribute as
private.

qubes/api/admin.py

@@ -1067,7 +1067,7 @@ class QubesAdminAPI(qubes.api.AbstractQubesAPI):
             non_default_attrs = set(attr for attr in dir(dev) if
                 not attr.startswith('_')).difference((
                     'backend_domain', 'ident', 'frontend_domain',
-                    'description', 'options'))
+                    'description', 'options', 'regex'))
             properties_txt = ' '.join(
                 '{}={!s}'.format(prop, value) for prop, value
                 in itertools.chain(

qubes/ext/pci.py

@@ -128,13 +128,13 @@ class PCIDevice(qubes.devices.DeviceInfo):
     # pylint: disable=too-few-public-methods
     regex = re.compile(
         r'^(?P<bus>[0-9a-f]+)_(?P<device>[0-9a-f]+)\.(?P<function>[0-9a-f]+)$')
-    libvirt_regex = re.compile(
+    _libvirt_regex = re.compile(
         r'^pci_0000_(?P<bus>[0-9a-f]+)_(?P<device>[0-9a-f]+)_'
         r'(?P<function>[0-9a-f]+)$')
 
     def __init__(self, backend_domain, ident, libvirt_name=None):
         if libvirt_name:
-            dev_match = self.libvirt_regex.match(libvirt_name)
+            dev_match = self._libvirt_regex.match(libvirt_name)
             assert dev_match
             ident = '{bus}_{device}.{function}'.format(**dev_match.groupdict())