Update exception thrown for keystore

When the keystore service is not available or
not initialized we do not want to crash the service.
So we throw and Exception that KeystoreService
is not availble when it should be possibly in an
incorrect state.

Test: atest CtsKeystoreTestCases
Bug: 304758094
Change-Id: If73856deb27b9f11a9b77f0ba32c3b4037332759