Call InitPartitionMetadata when resuming an update.

BootControlAndroid::InitPartitionMetadata() should always be called when
starting / resuming an update that uses dynamic partitions. This allows
updating the metadata for the target slot, as well as setting up the
internal state for accessing the dynamic partitions in the target slot.

Bug: 122097567
Test: Run update_engine_unittests on taimen and blueline.
Test: Apply a payload that uses dynamic partitions. Reboot before it
      finishes, then resume the update.
Change-Id: I1353f7460a61c0183654b6349689beaa9bf12129
diff --git a/common/constants.h b/common/constants.h
index 61e5ddd..d5a8ae3 100644
--- a/common/constants.h
+++ b/common/constants.h
@@ -41,7 +41,7 @@
 extern const char kPrefsCurrentUrlIndex[];
 extern const char kPrefsDailyMetricsLastReportedAt[];
 extern const char kPrefsDeltaUpdateFailures[];
-extern const char kPrefsDynamicPartitionMetadataInitialized[];
+extern const char kPrefsDynamicPartitionMetadataUpdated[];
 extern const char kPrefsFullPayloadAttemptNumber[];
 extern const char kPrefsInstallDateDays[];
 extern const char kPrefsLastActivePingDay[];