[storage-unittest] Trusty sleeps only if failed to open storage session

In current design, Trusty sleeps between open and close storage session.

There is no need to sleep when stroage test succeed to open session,
it is reasonable to sleep only if test case failed to open session.

Bug: 119111590
Change-Id: I7566849a68d4c73ab41f57c76371fd7932f9f825
1 file changed