set up the salt for partitions without build.prop

BUG:242954151

Test: make target-files-package, then check the two sha1 are same:
      1. sha1 of IMAGES/boot.img
      2. expected sha1 of boot in VENDOR/bin/install-recovery.sh

Test: make target-files-package; unzip target_files.zip IMAGES/\*`;
      `zip -d arget_files.zip IMAGES/\*`
      `add_img_to_target_files -a target_files.zip`.
      Verify that the rebuilt images are identical to the deleted ones.

Change-Id: I5906ac1696b6403674fd8330b1569aed53510945
diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 917e4dc..5196f63 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -861,6 +861,10 @@
         d["avb_{}_salt".format(partition)] = sha256(
             fingerprint.encode()).hexdigest()
 
+    # Set up the salt for partitions without build.prop
+    if build_info.fingerprint:
+      d["avb_salt"] = sha256(build_info.fingerprint.encode()).hexdigest()
+
     # Set the vbmeta digest if exists
     try:
       d["vbmeta_digest"] = read_helper("META/vbmeta_digest.txt").rstrip()