Copy TestHelper to TestHarness/test (make Gradle happy)

[aion-kelvin]

Gradle (and my IDE) didn't like that tests from test depended on a helper class from integration-test. Fixed it by just copying the helper class in question into test

Before fix:

> Task :TestHarness:compileTestJava FAILED
/home/sergiu/repos/node_test_harness/TestHarness/test/org/aion/harness/unit/KernelTest.java:6: error: package org.aion.harness.integ.resources does not exist
import org.aion.harness.integ.resources.TestHelper;
                                       ^
/home/sergiu/repos/node_test_harness/TestHarness/test/org/aion/harness/unit/KernelTest.java:15: error: cannot find symbol
    private static final String KEYSTORE_PATH = TestHelper.EXPECTED_BUILD_LOCATION + File.separator + TestHelper.DEFAULT_NETWORK + File.separator + "keystore";
                                                ^
  symbol:   variable TestHelper
  location: class KernelTest
/home/sergiu/repos/node_test_harness/TestHarness/test/org/aion/harness/unit/KernelTest.java:15: error: cannot find symbol
    private static final String KEYSTORE_PATH = TestHelper.EXPECTED_BUILD_LOCATION + File.separator + TestHelper.DEFAULT_NETWORK + File.separator + "keystore";
                                                                                                      ^
  symbol:   variable TestHelper
  location: class KernelTest
/home/sergiu/repos/node_test_harness/TestHarness/test/org/aion/harness/unit/KernelTest.java:20: error: cannot find symbol
        this.node = (JavaNode) TestHelper.configureDefaultLocalNodeForNetwork(Network.CUSTOM);
                               ^
  symbol:   variable TestHelper
  location: class KernelTest
4 errors

After fix:

sergiu@aion-XPS-8930:~/repos/node_test_harness$ ./gradlew clean build 

> Task :TestHarness:test
[LockHolder] Locking /var/lock/AionTestHarness/locktest_3059491 until I exit.

Deprecated Gradle features were used in this build, making it incompatible with Gradle 6.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/5.0/userguide/command_line_interface.html#sec:command_line_warnings

BUILD SUCCESSFUL in 12s
9 actionable tasks: 8 executed, 1 up-to-date

[aion-kelvin]

merged