Enable developer debugging for AVB-enabled devices

### modify build/unzip_boot/vbmeta.img.avb.json

* disable dm-verity hashtree verification
header -> flags: set to 1(AVB_VBMETA_IMAGE_FLAGS_HASHTREE_DISABLED = 1) to disable dm-verity hashtree(system/vendor etc.)

```diff
    "descriptors_size" : 1384,
    "rollback_index" : 0,
-   "flags" : 0,
+   "flags" : 1,
    "release_string" : "avbtool 1.0.0"
  },
  "authBlob" : {
```

* disable all AVB verification
header -> flags: set to 2(AVB_VBMETA_IMAGE_FLAGS_VERIFICATION_DISABLED = 2) to disable all verification, including AVB hash_footer(boot/recovery etc.) and dm-verity hashtree(system/vendor etc.)

```diff
    "descriptors_size" : 1384,
    "rollback_index" : 0,
-   "flags" : 0,
+   "flags" : 2,
    "release_string" : "avbtool 1.0.0"
  },
  "authBlob" : {
```

### unlock bootloader
'unlock' state will pass flag AVB_SLOT_VERIFY_FLAGS_ALLOW_VERIFICATION_ERROR when verifying images, then you can disable