sshd: add null check

* For some reason, privsep_pw->pw_passwd is null,
  and trying to run memset() and strlen() on that
  results in a segfault.
* Add a check for null to prevent that.

Change-Id: Ifd8edad787abf4fca481ccf6999bc2106027871a
start-ssh: use correct path for authorized_keys

* Also migrate keys from the old path.

Change-Id: I0810fe095a784cfb1c5fe2565068323e2679f2a9
Merge remote-tracking branch 'cm/cm-10.1' into HEAD