Tests: Add test for exported JARs

Add a unit test to test the new functions to export JAR targets. The
test builds three sub-projects: two that generate and export a JAR (one
does a build-directory-only export, one an install-only export), and a
third that consumes the first two as imported targets.

Tests/JavaExportImport/BuildExport/CMakeLists.txt

@@ -0,0 +1,10 @@
+project(foo Java)
+
+cmake_minimum_required (VERSION 3.5)
+set(CMAKE_VERBOSE_MAKEFILE 1)
+
+find_package(Java COMPONENTS Development)
+include(UseJava)
+
+add_jar(${PROJECT_NAME} Foo.java)
+export_jars(TARGETS ${PROJECT_NAME} FILE JavaBuildExportTestConfig.cmake)

Tests/JavaExportImport/BuildExport/Foo.java

@@ -0,0 +1,11 @@
+class Foo
+{
+  public Foo()
+  {
+  }
+
+  public void printName()
+  {
+    System.out.println("Foo");
+  }
+}