elog-gen.py : get inherited-from error

Openbmc error interfaces can inherit other error interfaces, thereby
allowing to combine metadata across errors. The current implementation
would support single inheritance only.

This first commit related to error inheritance implementation lets
elog-gen.py figure out an error's parent.

Change-Id: Ia5c44de755e777e0cb2725afa5988c97283d10f0
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
diff --git a/tools/example/xyz/openbmc_project/Example/Foo.errors.yaml b/tools/example/xyz/openbmc_project/Example/Foo.errors.yaml
index 73fe62b..5ab311f 100644
--- a/tools/example/xyz/openbmc_project/Example/Foo.errors.yaml
+++ b/tools/example/xyz/openbmc_project/Example/Foo.errors.yaml
@@ -1,2 +1,4 @@
 - name: Foo
   description: this is test error Foo
+  inherits:
+      - example.xyz.openbmc_project.Example.TestErrorOne