Avoid moreTest task on gradle build -x test build

[fvasco]

Allow build without test if JDK_16 environment variable is not set ( #291)

[elizarov]

I've tried doing it like this. The problem is that you loose ability to use Gradle test runner IDEA properly and otherwise run single test from Gradle, because with this change gradle test --tests <test-name> runs both test and moreTest. I don't know a workaround, so I've defined moreTest. The downside is that if you want to run w/o tests you have to do grade build -x test -x moreTest

[qwwdfsad]

Current workaround is to make JDK_16 point to JDK_HOME, updated readme