Assignment to reserved built-in symbol

Built-in symbol: file, format, range etc was re-assigned as local vars
in files: test/functional/swift_test_client.py and
test/functional/tests.py, rename these local vars.

Fixes bug #1208078

Change-Id: I627894cd722bd32cad231d534cbe97a0412c7cc9
Merge "Assignment to reserved built-in symbol"