track "first" OR_CONN

Right now the first stages of the "first" OR_CONN get reported as BOOTSTRAP_STATUS_CONN_DIR and BOOTSTRAP_STATUS_HANDSHAKE (the latter is a special bootstrap phase that gets translated into BOOTSTRAP_STATUS_HANDSHAKE_DIR or BOOTSTRAP_STATUS_HANDSHAKE_OR depending on how much progress was previously reported. The logic in functions that report these events should be moved up to a new abstraction so lower level code has to track less high-level state.

This also eliminates some logic in control_event_bootstrap() that tries to figure out whether a given handshake attempt corresponds to a directory connection or an application circuit connection.