Most jpackage tests are in the default package. Some are in the "jdk.jpackage.tests" package for no specific reason. All jpackage tests should be in the same (the default) package.

The positive side effect of this change is shortening jtreg directory names from "jtreg_open_test_jdk_tools_jpackage_share_jdk_jpackage_tests_BasicTest_java" to "jtreg_open_test_jdk_tools_jpackage_share_BasicTest_java". This will reduce the risk of lengths of jtreg paths exceeding the limit of 260 chars on Windows.