Jefftree: Fix bug around low steps for exponential backoff

JobBuild
172
02-23 23:59
pull-apiserver-network-proxy-docker-build-all 1379105756200046592 1366830825257046016 1366830485975601152 1364662047295410176 1364364285639135232
pull-apiserver-network-proxy-test 1379105756174880768 1366830825215102976 1366830485895909376 1364662047249272832 1364364285597192192