Get rid of misleading SCHEMA_INFO error

Get rid of misleading SCHEMA_INFO error

During startup the key-manager attempts to read a table SCHEMA_INFO to get the
information about the database version. In older versions of the database that
table is missing. Key-manager properly handles that case but produces 3 lines of
error log which may suggest that something went wrong.

This commit checks the existence of the table before attempting to use it. Whole
operation is enclosed in a transaction.

Change-Id: Ie7f1fbe1182c2add5965f8e5ddada262ffcb42fe