Keep JavaBasePlugin ability to run a single test

In normal 'java' project you can pass a runtime parameters to run a single test e.g. 
`-Dtest.single=AdditionOperationTest`

To respect this we can override the include pattern only if that property is not set.

https://github.com/gradle/gradle/blob/530b2a4609c0b512711e53fede5dca58254dd6ad/subprojects/plugins/src/main/groovy/org/gradle/api/plugins/JavaBasePlugin.java#L262