The message field of ExecuteOperationResponse should not be "undefined"

As marked in ExecuteOperationCommandITest, https://github.com/hawkular/hawkular-agent/blob/master/hawkular-agent-itest-parent/hawkular-agent-itest/src/test/java/org/hawkular/cmdgw/ws/test/ExecuteOperationCommandITest.java#L93
the ExecuteOperationCommand returns "undefined" in the ExecuteOperationResponse in case the operation was successful. "undefined" in the response makes no sense and needs to be replaced by some meaningful message.

The simplest solution would be to change this line https://github.com/hawkular/hawkular-agent/blob/master/hawkular-wildfly-monitor/src/main/java/org/hawkular/agent/monitor/cmd/ExecuteOperationCommand.java#L143 to write something meaningful into the response.

But the preferred solution is to refactor ExecuteOperationCommand to
(1) extend AbstractResourcePathCommand and
(2) use OperationBuilder in the same way as it is used in several other commands ( AddDatasourceCommand, AddJdbcDriverCommand, UpdateDatasourceCommand ... )

As a result of the refactoring, the response message will be written by org.hawkular.agent.monitor.cmd.AbstractResourcePathCommand.success(BasicMessageWithExtraData<REQ>, RESP) https://github.com/hawkular/hawkular-agent/blob/master/hawkular-wildfly-monitor/src/main/java/org/hawkular/agent/monitor/cmd/AbstractResourcePathCommand.java#L194-L197

To run the build of the agent project with integration tests, use mvn clean install -Pitests