ActivityManager: Make bootcomplete marker failure a warning

This isn't terminal, and currently even expected in some cases.
Make it a warning instead of an error.

Bug: 26978865
Change-Id: Ieb7f29e340f5b08f69887b9f094554858fb72786

services/core/java/com/android/server/am/ActivityManagerService.java

@@ -6598,7 +6598,8 @@ public final class ActivityManagerService extends ActivityManagerNative
                 try {
                     mInstaller.markBootComplete(VMRuntime.getInstructionSet(abi));
                 } catch (InstallerException e) {
-                    Slog.e(TAG, "Unable to mark boot complete for abi: " + abi, e);
+                    Slog.w(TAG, "Unable to mark boot complete for abi: " + abi + " (" +
+                            e.getMessage() +")");
                 }
                 completedIsas.add(instructionSet);
             }