Before all CA related commands can succeed, the CA table needs to
be populated. This patch invokes code to refresh the table as
Barbican starts.
In addition, the CA table entries can expire over time, to ensure
GET /cas always returns current values, the table is refreshed as
necessary at that time too.
I also added created a session for this routine to ensure any
updates are written immediately to the database.
Change-Id: I0e6f9aec073c897f811b0b87a16db3b52753d734
Closes-bug: #1495576
91a561dd9a