wifi: allow setclient to join hidden networks

By default, wpa_supplicant doesn't scan SSIDs with specific Probe
Request frames - it only uses a broadcast SSID.

This makes it impossible to join hidden networks. Fix this, since our
setup network will usually be hidden and our primary networks may be
hidden by customers at will.

Also, remove dependency on `wpa_passphrase` and start computing the
passphrase in Python. This avoids complicated string edits.

Change-Id: Ia0bd19c20a0a04f1cc030e33eae32aca363c3908
3 files changed