[generate_asic_config_checksum.py] Convert to Python 3 (#5783)

- Convert script to Python 3
    - Need to open file in binary mode before hashing due to new string data type in Python 3 being unicode by default. This should probably have been done regardless.
- Reorganize imports alphabetically
- When running the script, don't explicitly call `python`. Instead let the program loader use the interpreter specified in the shebang (which is now `python3`).

build_debian.sh

@@ -463,7 +463,8 @@ EOF
 sudo cp ./files/scripts/core_cleanup.py $FILESYSTEM_ROOT/usr/bin/core_cleanup.py
 
 ## Copy ASIC config checksum
-python files/build_scripts/generate_asic_config_checksum.py
+sudo chmod 755 files/build_scripts/generate_asic_config_checksum.py
+./files/build_scripts/generate_asic_config_checksum.py
 if [[ ! -f './asic_config_checksum' ]]; then
     echo 'asic_config_checksum not found'
     exit 1

files/build_scripts/generate_asic_config_checksum.py

@@ -1,8 +1,8 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
-import syslog
-import os
 import hashlib
+import os
+import syslog
 
 SYSLOG_IDENTIFIER = 'asic_config_checksum'
 
@@ -45,7 +45,7 @@ def generate_checksum(checksum_files):
     checksum = hashlib.sha1()
     for checksum_file in checksum_files:
         try:
-            with open(checksum_file, 'r') as f:
+            with open(checksum_file, 'rb') as f:
                 for chunk in iter(lambda: f.read(CHUNK_SIZE), b""):
                     checksum.update(chunk)
         except IOError as e: