Handle ServiceSpecificException in openSession

In MediaCas#openSession(int, int), the ServiceSpecificException is
caught and thrown as an IllegalStateException. This is inconsistent with
the documentation of the method. Correct it to throw a MediaCasException.

Bug: 409937172
Test: atest CtsMediaMiscTestCases
Flag: EXEMPT bugfix
Change-Id: I02cf600f16f9ee5839888cd6c1770fe462f21992