releasetools: Ignore nonexistent APEX overrides.

This allows sharing the same signing config on different target_files
zips. Nonexistent APEX will be ignored with a warning.

Bug: 137249701
Test: Run sign_target_files_apks with APEX overrides.
Change-Id: I2bad0f5c00753ed36ec5ae3431c7dc2ff1fc3e9c
(cherry picked from commit b369c7226a)

tools/releasetools/sign_target_files_apks.py

@@ -185,6 +185,9 @@ def GetApexKeys(keys_info, key_map):
   for apex, key in OPTIONS.extra_apex_payload_keys.items():
     if not key:
       key = 'PRESIGNED'
+    if apex not in keys_info:
+      logger.warning('Failed to find %s in target_files; Ignored', apex)
+      continue
     keys_info[apex] = (key, keys_info[apex][1])
 
   # Apply the key remapping to container keys.