Ensure that tests compile as-is before stripping annotations (#408)

+ bookstore: add missing import statement in tests

bin/journey-test.sh

     cp -R -H ${xjava}/exercises/${exercise}/src/example/java/* ${exercism_exercises_dir}/java/${exercise}/src/main/java/
 
     pushd ${exercism_exercises_dir}/java/${exercise}
+    # Check that tests compile before we strip @Ignore annotations
+    gradle compileTestJava
     # Ensure we run all the tests (as delivered, all but the first is @Ignore'd)
     for testfile in `find . -name "*Test.java"`; do
       sed 's/@Ignore//' ${testfile} > "${tempfile}" && mv "${tempfile}" "${testfile}"

exercises/book-store/src/test/java/BookstoreTest.java

 import java.util.ArrayList;
 import java.util.Arrays;
 
+import org.junit.Ignore;
 import org.junit.Test;
 
 public class BookstoreTest{