Ensure all connections are closed on failure

[ckunki]

Ticket mentioned as "IntRef" reported that when user cancels an SQL query in Exasol database the resulting Hive query does not get canceled.

The current ticket therefore requests to inspect and if possible to improve the connection handling in VSHIVE.
See also ticket exasol/virtual-schema-common-jdbc#151 for improved connection handling in VSCJDBC.

If possible then VSHIVE should ensure that especially in the case of an exception VSHIVE closes all connections.

Acceptance criteria

1. Connection handling in VSHIVE is analysed and result of analysis is attached or linked to the current ticket
2. If possible connection handling is improved

See for example HiveSqlDialect.java#L144

@Override
protected RemoteMetadataReader createRemoteMetadataReader() {
    try {
        return new HiveMetadataReader(this.connectionFactory.getConnection(), this.properties);
    } catch (final SQLException exception) {
        throw new RemoteMetadataReaderException(ExaError.messageBuilder("E-VSHIVE-1")
                .message("Unable to create Hive remote metadata reader. Caused by: {{cause|u}}",
                        exception.getMessage()) //
                .toString(), exception);
    }
}

[Shmuma]

All the issues are in shared libs (virtual schema-common-jdbc). All the findings and subsequent task are in this ticket: exasol/virtual-schema-common-jdbc#151

[kaklakariada]

Reviewed OK. Implementation will be done in follow-up tickets.