storage: add Volume.ephemeral property

QubesOS/qubes-issues#904

qubesadmin/storage.py

@@ -164,6 +164,21 @@ def rw(self, value):
         self._qubesd_call('Set.rw', str(value).encode('ascii'))
         self._info = None
 
+    @property
+    def ephemeral(self):
+        """True if volume is read-write."""
+        try:
+            self._fetch_info()
+        except qubesadmin.exc.QubesDaemonAccessError:
+            raise qubesadmin.exc.QubesPropertyAccessError('ephemeral')
+        return self._info.get('ephemeral', 'False') == 'True'
+
+    @ephemeral.setter
+    def ephemeral(self, value):
+        """Set rw property"""
+        self._qubesd_call('Set.ephemeral', str(value).encode('ascii'))
+        self._info = None
+
     @property
     def snap_on_start(self):
         """Create a snapshot from source on VM start."""