Add support for vtable flags for methods

This adds support for specifying the vtable flags
SD_BUS_VTABLE_DEPRECATED, SD_BUS_VTABLE_HIDDEN,
SD_BUS_VTABLE_UNPRIVILEGED and SD_BUS_VTABLE_METHOD_NO_REPLY for
methods. The list of flags in the YAML file will be ORed together.

Change-Id: I7762ffb15a1483760f3b7e0ea02e80fd52ebd9b9
Signed-off-by: Waqar Hameed <waqarh@axis.com>
diff --git a/example/net/poettering/Calculator.interface.yaml b/example/net/poettering/Calculator.interface.yaml
index 6e44093..a942f5c 100644
--- a/example/net/poettering/Calculator.interface.yaml
+++ b/example/net/poettering/Calculator.interface.yaml
@@ -42,6 +42,9 @@
       errors:
         - self.Error.DivisionByZero
     - name: Clear
+      flags:
+        - unprivileged
+        - no_reply
       description: >
         Reset the LastResult property to zero.
 properties: