property: Add errors support

Add errors support for properties.

Closes openbmc/openbmc#1641

Tested: Verified that when an interface threw a defined property
error, the generated code caught it and returned an error to
the REST call.

Change-Id: I8cb8c77995026f12e373291822e4e0a623a84d81
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/example/net/poettering/Calculator.errors.yaml b/example/net/poettering/Calculator.errors.yaml
index 730e2a3..b2f6ee3 100644
--- a/example/net/poettering/Calculator.errors.yaml
+++ b/example/net/poettering/Calculator.errors.yaml
@@ -1,3 +1,6 @@
 - name: DivisionByZero
   description: >
     An attempt to divide by zero was attempted.
+- name: PermissionDenied
+  description: >
+    The user does not have enough privileges to perform the operation.