Further enhancements of integration testing

[mvicsokolova]

• [ ] check Native and JS/IR klibs for atomicfu references using klib utility that will be introduced in 2.0:

<KOTLIN_NATIVE_HOME>/bin/klib dump-ir-signatures <klib file>

• [ ] mavenTest task directly depends on :atomicfu local publication task, which should be avoided. Create separate tasks for publication of atomicfu and atomicfu-gradle-plugin artifacts to the custom local repo in the build directory.
• [ ] mavenTest and functionalTest should not cache the previous build results: the last changes in atomicfu-gradle-plugin should be encountered (for now it's done via outputs.upToDateWhen { false }).
• [x] Remove old "integration" tests from atomicfu-gradle-plugin/test/
• [ ] KlibChecker: try to add kotlin.native.home path to the classpath and invoke klib utility without reflection (or at least with a ProcessBuilder)
• [ ] Refrain from using mavenLocal() repo in integaration test projects, publish artifacts to the custom local repo instead.