Fix linter failures in nav2_bt_navigator

[crdelsey]

Test project /home/crdelsey/src/ros_dev_workspace/navigation2/build/nav2_bt_navigator
Start 1: copyright
1/5 Test #1: copyright ........................ Passed 0.46 sec
Start 2: cppcheck
2/5 Test #2: cppcheck ......................... Passed 0.46 sec
Start 3: cpplint
3/5 Test #3: cpplint .......................... Passed 0.50 sec
Start 4: lint_cmake
4/5 Test #4: lint_cmake .......................***Failed 0.45 sec
Start 5: uncrustify
5/5 Test #5: uncrustify ....................... Passed 0.49 sec

80% tests passed, 1 tests failed out of 5