marlin/sailfish: Fix adb doesn't remember computer authorization

In init.common.diag.rc, make a backup of /data/misc/adb/adb_keys
if it exists, copy the OEM adb_keys to /data/misc/adb/adb_keys,
then copy the backup if it exists back to /data/misc/adb/adb_keys.
This ensures that the OEM keys will always be present and new keys
added by users will also be saved.

Change-Id: I3e2a08936b9e961ac9eb25e2f06859a557ab0fd6

init.common.diag.rc.userdebug

@@ -4,8 +4,13 @@ on post-fs-data
     # Modem logging collection
     mkdir /data/diag_logs 0777 system system
 
-    # Create symlink for OEM adb_keys
-    symlink /vendor/etc/adb_keys /data/misc/adb/adb_keys
+    # Copy OEM adb_keys if /data/misc/adb/adb_keys does not exist
+    copy /data/misc/adb/adb_keys /data/misc/adb/adb_keys_temp
+    copy /vendor/etc/adb_keys /data/misc/adb/adb_keys
+    copy /data/misc/adb/adb_keys_temp /data/misc/adb/adb_keys
+    chown system shell /data/misc/adb/adb_keys
+    chmod 640 /data/misc/adb/adb_keys
+    rm /data/misc/adb/adb_keys_temp
 
 on boot
     chmod 666 /dev/diag