Issue 62 - Prepare SPI tester framework

* Create SPI tester framework
 * new module spi-tester
 * new source set for spi test code
* Setup example framework use for Store SPI

This does not complete issue #62, only prepares the next step for it.
Gradle by default doesn't show stdout/stderr of the tests. You have to run gradle with -i to get INFO logging. Or we can add this to gradle build file to force it (this is equivalent to Maven default behavior)

test {
    testLogging {
        events "passed", "skipped", "failed", "standardOut", "standardError"
    }
}