Don't proactively close source executions under a transaction scope higher than request

Under a transaction we are always closing source executions that are typically held open for lobs. While this is basically required in the request scope (as close is too late for a commit - the client would not receive a failure notification), it should not be needed in the other transaction scopes.

For lobs that are not readable after close currently will be seen as unreabable values from Teiid.