Hikari and Commons DBCP2 are already validating that the connection is
valid before borrowing it from the pool. This commit makes that behaviour
consistent by enabling that feature for the Tomcat and Commons DBCP data
sources.
Since a validation query is required in those cases, the infrastructure
of `DataSourceHealthIndicator` has been merged in a single place: the
`DatabaseDriver` enum provides not only the driver class names but also
the validation query, if any.
Closes gh-4906
1f106ddf8c