Shade test jars from compiler used in Gradle tests

This fixes `VerifyError` for all integration tests calling
`KotlinTestUtils.findAndroidSdk()`.
The exception was thrown because `:kotlin-gradle-plugin-integration-tests`
was depending on both relocated intellij-core (from kotlin-compiler-embeddable)
and non-relocated intellij-core (transitevely through tests jars from compiler).

A call to `findAndroidSdk()` was triggering classloading
for `KotlinTestUtils` which had bytecode references to
`org.jetbrains.kotlin.idea.KotlinLanguage` loaded from the embeddable compiler
and to `com.intellij.lang.Language` loaded from non-relocated intellij-core.

`KotlinLanguage` from the embeddable compiler was a subclass of relocated
`org.jetbrains.kotlin.com.intellij.lang.Language` thus it was not
assignable to `com.intellij.lang.Language` causing `VerifyError`.

The solution is to create relocated jar combining the necessary test jars
from the compiler.

libraries/tools/kotlin-gradle-plugin-test-utils-embeddable/build.gradle.kts

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+
+import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
+import org.gradle.jvm.tasks.Jar
+
+description = "Shaded test jars from compiler for Gradle integration tests"
+
+plugins { `java` }
+
+val packedJars by configurations.creating
+
+val projectsToInclude = listOf(":compiler:tests-common",
+                               ":compiler:incremental-compilation-impl",
+                               ":kotlin-build-common")
+
+dependencies {
+    for (projectName in projectsToInclude) {
+        packedJars(projectTests(projectName)) { isTransitive = false }
+    }
+
+    packedJars(intellijDep()) { includeJars("idea_rt") }
+
+}
+
+runtimeJar(rewriteDepsToShadedCompiler(
+    task<ShadowJar>("shadowJar")  {
+        from(packedJars)
+    }
+))