The shell may add extra output beyond the intended content, but the
shell-test was only looking for exact match.  Extra output may
include whitespace and/or an echo of the command itself.

This reworks the shell test to allow for this extra output, as long
as the intended string appears in the content of the file it will
pass.

Replaces the separate "Initialized" and "Shutdown" flags with a single
state flag.  This simplifies things and makes for a single source
of truth for the state of OSAL globally.

In particular this allows for:
- Multiple invocations of OS_API_Init() - subsequent calls can be ignored
- Deleting of any internal objects that did get created if OS_API_Init() fails
  (leaves system in same state as when it started)
- Allows Re-initialization of OSAL after OS_ApplicationShutdown() - may be
  relevant when running unit tests several times without rebooting.

This cleans up all OSAL resources as best as possible, ideally leaving
the system in a state where OS_API_Init() may be invoked again.

Invoke OS_API_Teardown to reset state for next test

Fix #871, allow OSAL re-initialization

Fix #944, add OS_API_Teardown

Fix #939, rework shell test