update_engine: Add powerwash flag to update status

Add a powerwash flag to the update status which is set to true if and
only if a powerwash takes place. This will ensure that the user is
informed of a pending powerwash exactly when it is going to happen.

BUG=chromium:1070563
TEST=FEATURES=test emerge-amd64-generic update_engine
channel change and update on test device

Cq-Depend: chromium:2187671
Change-Id: I58314ecc7c9c2e64c906ef5b31cb780948196296
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/2187672
Reviewed-by: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Tested-by: Miriam Polzer <mpolzer@google.com>
Commit-Queue: Miriam Polzer <mpolzer@google.com>
diff --git a/update_status_utils_unittest.cc b/update_status_utils_unittest.cc
index e3dd037..228201c 100644
--- a/update_status_utils_unittest.cc
+++ b/update_status_utils_unittest.cc
@@ -35,6 +35,7 @@
       .new_version = "12345.0.0",
       .is_enterprise_rollback = true,
       .is_install = true,
+      .will_powerwash_after_reboot = true,
   };
   string print =
       R"(CURRENT_OP=UPDATE_STATUS_CHECKING_FOR_UPDATE
@@ -44,6 +45,7 @@
 NEW_SIZE=888
 NEW_VERSION=12345.0.0
 PROGRESS=0.5
+WILL_POWERWASH_AFTER_REBOOT=true
 )";
   EXPECT_EQ(print, UpdateEngineStatusToString(update_engine_status));
 }