Convert parse error to text type

Some local environments (but not yet the gate) are experiencing
failure of InstantiationDataTest.test_format_parse_invalid_message.

This change fixes that test by converting the parse exception to
a text type before including it in the error message.

Change-Id: I06e271559e27452a7a0c1e8807a37bb5ed5df2fa
Closes-Bug: #1365880
Merge "Convert parse error to text type"