fastbootd: Disallow certain operations during snapshot updates.

When a snapshot is applied or is merging, requests to erase or flash
userdata, metadata, or misc must be protected. In addition, the
set_active command must be restricted when a merge is in progress.

In addition, introduce a "snapshot-update merge" command for assisting
with erase requests when a merge is in progress. As in recovery, this
will force a merge to complete.

Bug: 139154945
Test: apply update
      fastboot erase userdata
      fastboot erase metadata
      fastboot erase misc
      fastboot set_active

Change-Id: I152446464335c62c39ffb4cc6366be9de19eac30
diff --git a/fastboot/device/variables.cpp b/fastboot/device/variables.cpp
index 6e613d6..91fc84c 100644
--- a/fastboot/device/variables.cpp
+++ b/fastboot/device/variables.cpp
@@ -432,19 +432,13 @@
                              std::string* message) {
     // Note that we use the HAL rather than mounting /metadata, since we want
     // our results to match the bootloader.
-    auto hal = device->boot_control_hal();
+    auto hal = device->boot1_1();
     if (!hal) {
         *message = "not supported";
         return false;
     }
 
-    android::sp<IBootControl1_1> hal11 = IBootControl1_1::castFrom(hal);
-    if (!hal11) {
-        *message = "not supported";
-        return false;
-    }
-
-    MergeStatus status = hal11->getSnapshotMergeStatus();
+    MergeStatus status = hal->getSnapshotMergeStatus();
     switch (status) {
         case MergeStatus::SNAPSHOTTED:
             *message = "snapshotted";