[Python] Align files in root dir, dockers/ and files/ with PEP8 standards (#6109)

**- Why I did it**

Align style with slightly modified PEP8 standards (extend maximum line length to 120 chars). This will also help in the transition to Python 3, where it is more strict about whitespace, plus it helps unify style among the SONiC codebase. Will tackle other directories in separate PRs.

**- How I did it**

Using `autopep8 --in-place --max-line-length 120` and some manual tweaks.

files/build_scripts/generate_asic_config_checksum.py

@@ -14,16 +14,19 @@ CONFIG_FILES = {
 
 OUTPUT_FILE = os.path.abspath('./asic_config_checksum')
 
+
 def log_info(msg):
     syslog.openlog(SYSLOG_IDENTIFIER)
     syslog.syslog(syslog.LOG_INFO, msg)
     syslog.closelog()
 
+
 def log_error(msg):
     syslog.openlog(SYSLOG_IDENTIFIER)
     syslog.syslog(syslog.LOG_ERR, msg)
     syslog.closelog()
 
+
 def get_config_files(config_file_map):
     '''
     Generates a list of absolute paths to ASIC config files.
@@ -34,11 +37,12 @@ def get_config_files(config_file_map):
             config_files.append(os.path.join(path, config_file))
     return config_files
 
+
 def generate_checksum(checksum_files):
     '''
     Generates a checksum for a given list of files. Returns None if an error
     occurs while reading the files.
-    
+
     NOTE: The checksum is performed in the order provided. This function does 
     NOT do any re-ordering of the files before creating the checksum.
     '''
@@ -54,6 +58,7 @@ def generate_checksum(checksum_files):
 
     return checksum.hexdigest()
 
+
 def main():
     config_files = sorted(get_config_files(CONFIG_FILES))
     checksum = generate_checksum(config_files)
@@ -63,5 +68,6 @@ def main():
     with open(OUTPUT_FILE, 'w') as output:
         output.write(checksum + '\n')
 
+
 if __name__ == '__main__':
     main()