tests: do not ignore stderr of vty_test, also match it

This change is needed for I4e27d6e89d3f851b5ea4f00da01e7093afa537b2.

Change-Id: Ia601ecd2e69aeb6669e0e2e5dd60135a751611e7
diff --git a/tests/vty/vty_test.err b/tests/vty/vty_test.err
new file mode 100644
index 0000000..8ad4fd9
--- /dev/null
+++ b/tests/vty/vty_test.err
@@ -0,0 +1,61 @@
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 1
+Got VTY event: 3
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 1
+Got VTY event: 2
+Got VTY event: 3
+There is no such command.
+Error occurred during reading the below line:
+ level1 b
+
+Inconsistent indentation -- leading whitespace must match adjacent lines, and
+indentation must reflect child node levels. A mix of tabs and spaces is
+allowed, but their sequence must not change within a child block.
+Error occurred during reading the below line:
+ level1 b
+
+Inconsistent indentation -- leading whitespace must match adjacent lines, and
+indentation must reflect child node levels. A mix of tabs and spaces is
+allowed, but their sequence must not change within a child block.
+Error occurred during reading the below line:
+	 	child1 b
+
+Error occurred during reading the below line:
+return-warning
+
+% Ignoring deprecated 'logging level depr (debug|info|notice|error|fatal)'
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 1
+Got VTY event: 3
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 2
+Got VTY event: 1
+Got VTY event: 3