lock.lock_many(): use passed os_{type,version}, not ctx

Affects teuthology --lock with os_{type,version} in the yaml.

Fixes: #9811
Signed-off-by: Dan Mick <dan.mick@inktank.com>
task.ssh_keys(): manage authorized_keys, not keys2

See the issue for a description, but authorized_keys2 is dead
on RHEL7 and dying elsewhere.

Fixes: #9812
Signed-off-by: Dan Mick <dan.mick@inktank.com>
Merge pull request #343 from ceph/wip-dmick

Fixes for #9811 and #9812