I have the same problem attempting to install on Ubuntu 12.04. The password less ssh has been setup. From the ambari server I can use ssh root@hadoopmaster and ssh root@hadoopmaster.remusbear.net without needing to provide a password.
==========================
Creating target directory…
==========================
Command start time 2015-01-10 18:52:47
Permission denied (publickey,password).
SSH command execution finished
host=hadoopmaster.remusbear.net, exitcode=255
Command end time 2015-01-10 18:52:47
ERROR: Bootstrap of host hadoopmaster.remusbear.net fails because previous action finished with non-zero exit code (255)
ERROR MESSAGE: Permission denied (publickey,password).
STDOUT:
Permission denied (publickey,password).
Any further ideas what we are doing wrong?