update_engine: Increase periodic update check read allows

Delete the periodic update check interval marker file after 6 attempts
at reading it instead of the previous 3 so the auto updater tests can do
more interesting things with it.

BUG=chromium:953471
TEST=sudo FEATURES=test emerge update_engine

Change-Id: I1a67fc5dadfd1ae0fde1308e398e6eb21171df05
Reviewed-on: https://chromium-review.googlesource.com/c/aosp/platform/system/update_engine/+/2393098
Tested-by: Amin Hassani <ahassani@chromium.org>
Auto-Submit: Amin Hassani <ahassani@chromium.org>
Reviewed-by: David Haddock <dhaddock@chromium.org>
Commit-Queue: David Haddock <dhaddock@chromium.org>
diff --git a/update_manager/real_updater_provider.cc b/update_manager/real_updater_provider.cc
index 268f3bb..8465718 100644
--- a/update_manager/real_updater_provider.cc
+++ b/update_manager/real_updater_provider.cc
@@ -460,7 +460,7 @@
     if (prefs_ && prefs_->Exists(key) && prefs_->GetInt64(key, &result)) {
       // This specific value is used for testing only. So it should not be kept
       // around and should be deleted after a few reads.
-      if (++read_count_ > 2)
+      if (++read_count_ > 5)
         prefs_->Delete(key);
 
       // Limit the timeout interval to 10 minutes so it is not abused if it is