common-mk: Add report_requisition to IUSE flags that default false.

Flag to enable reporting requisition in update_engine.

BUG=chromium:1307518,b:180112731
TEST=USE-flag change only

Cq-Depend: chromium:3542571, chromium:3542595
Change-Id: I7a56aa44f228e3058e42f023f94b1a78f07e8308
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/3538206
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Kyle Williams <kdgwill@chromium.org>
Commit-Queue: Kyle Williams <kdgwill@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform2/+/3543626
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
diff --git a/common-mk/platform2.py b/common-mk/platform2.py
index 6b617a0..6eaf437 100755
--- a/common-mk/platform2.py
+++ b/common-mk/platform2.py
@@ -118,6 +118,7 @@
     'prjquota',
     'profiling',
     'qrtr',
+    'report_requisition',
     'selinux',
     'slow_mount',
     'systemd',