update_repository: Fix some warnings reported by pylint

 W: 47,0: Unused import platform
 W: 49,0: Unused import shutil
 W: 65,4:setup_argument_parser: Redefining name 'parser' from outer scope (line 304)
 W:124,47:update_repository: Redefining name 'components_to_update' from outer scope (line 333)
 W:272,35:parse_components_from_argument: Redefining name 'caller_arguments' from outer scope (line 306)
 C:304,4: Invalid name "parser" for type constant (should match (([A-Z_][A-Z0-9_]*)|(__.*__))$)
 C:306,4: Invalid name "caller_arguments" for type constant (should match (([A-Z_][A-Z0-9_]*)|(__.*__))$)
 C:333,4: Invalid name "components_to_update" for type constant (should match (([A-Z_][A-Z0-9_]*)|(__.*__))$)
 C:336,8: Invalid name "components_to_update" for type constant (should match (([A-Z_][A-Z0-9_]*)|(__.*__))$)
 C:338,8: Invalid name "components_to_update" for type constant (should match (([A-Z_][A-Z0-9_]*)|(__.*__))$)

Change-Id: I0bcc27c183f01b861c7136291555f1064834d0d2
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>