Improve error reporting for backend import failures

Use import_module instead of try_import so that any import exception
includes a full stack trace and the original error message.

Change-Id: I64449688f22a224b590807317472f26e64f377a3
Updated from global requirements

Change-Id: Ia7f6ff57a5792d39608d6fcf4490c99a19ea8afb
Merge "Improve error reporting for backend import failures"
Merge "Updated from global requirements"