Fix 3.2 jstest stepUp functions

These stepUp functions appear in:
write_concern_after_stepdown.js
read_committed_stale_history.js
double_rollback.js
double_rollback_early.js
rollback_with_socket_error_steady_state.js
write_concern_after_stepdown_and_stepup.js.

These all try to accomplish the same thing but have different implementations. There should be one stepUp function that makes sure all nodes are electable after it returns. https://github.com/mongodb/mongo/commit/3823a20f0186d0e6b544212fb423f9f0ef786235 contains an example of how this can look.

Alternatively, we could backport SERVER-20844 to 3.2 to make this unnecessary.