Renamed “InstalledModuleDescriptorPlugin" to “SystemModuleDescriptorPlugin” (jdk/tools/jlink/internal/plugins/SystemModuleDescriptorPlugin.java) before jigsaw was integrated to jdk9.

We also need to rename the directory “InstalledModuleDescriptors” (test/tools/jlink/plugins/InstalledModuleDescriptors) and any reference to “installed” to “system” in the tests.