Lazy initialization of ImageReader breaks rmid

Latest jigsaw refresh had an optimization to load of the system ImageReader lazily, which breaks rmid [1]. This needs to be backed out to stabilize builds:

diff -r 32cb9898b630 src/java.base/share/classes/jdk/internal/module/ModuleBootstrap.java
--- a/src/java.base/share/classes/jdk/internal/module/ModuleBootstrap.java Thu Feb 16 17:05:48 2017 +0100
+++ b/src/java.base/share/classes/jdk/internal/module/ModuleBootstrap.java Thu Feb 16 17:08:12 2017 +0100
@@ -115,12 +115,7 @@
         long t0 = System.nanoTime();
 
         // system modules (may be patched)
- ModuleFinder systemModules;
- if (SystemModules.MODULE_NAMES.length > 0) {
- systemModules = SystemModuleFinder.getInstance();
- } else {
- systemModules = ModuleFinder.ofSystem();
- }
+ ModuleFinder systemModules = ModuleFinder.ofSystem();
 
         PerfCounters.systemModulesTime.addElapsedTimeFrom(t0);
 
[1] http://mail.openjdk.java.net/pipermail/core-libs-dev/2017-February/046478.html