Hacktoberfest: Python 3 compatibility issues

[flake8](http://flake8.pycqa.org) testing of https://github.com/ArduPilot/SiK on Python 3.7.1

$ __flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics__
```
./Firmware/tools/check_code.py:17:13: E999 SyntaxError: invalid syntax
print sys.argv
^
./Firmware/tools/bank-alloc.py:143:31: E999 SyntaxError: invalid syntax
print "Failed to allocate", module[0], "with size", module[1], \
^
./Firmware/tools/update_mode.py:35:12: F821 undefined name 'pexpect'
except pexpect.TIMEOUT:
^
./Firmware/tools/atcommander.py:269:81: E999 SyntaxError: invalid syntax
print "Please specify a --list-* or --set-* operation (try -h if unsure)"
^
./Firmware/tools/rssi.py:51:31: E999 TabError: inconsistent use of tabs and spaces in indentation
sys.stdout.flush()
^
./Firmware/tools/uploader.py:100:31: E999 TabError: inconsistent use of tabs and spaces in indentation
if use_mavlink:
^
5 E999 SyntaxError: invalid syntax
1 F821 undefined name 'pexpect'
6
```
__E901,E999,F821,F822,F823__ are the "_showstopper_" [flake8](http://flake8.pycqa.org) issues that can halt the runtime with a SyntaxError, NameError, etc. These 5 are different from most other flake8 issues which are merely "style violations" -- useful for readability but they do not effect runtime safety.
* F821: undefined name `name`
* F822: undefined name `name` in `__all__`
* F823: local variable name referenced before assignment
* E901: SyntaxError or IndentationError
* E999: SyntaxError -- failed to compile a file into an Abstract Syntax Tree

Run the flake8 command from the issue with Python 3.7.1 and inspect Firmware/tools/check_code.py, bank-alloc.py, update_mode.py, atcommander.py, rssi.py, and uploader.py. Resolve the listed Python 3 syntax, indentation, and undefined-name errors, then rerun the same showstopper checks and confirm they report no E901, E999, or F821 issues.

Written by the indexing model from the issue text.