Can you confirm that that gtsai account exists on the target node? This looks like an authentication issue on the node you're trying to bootstrap. Can you ssh directly into 134.79.129.170 as gtsai with either your password, or the specified ssh key?
Strange... That should be essentially exactly what knife is doing. What OSes are these? From your workstation (which is where you should be attempting the knife bootstrap command from), run this command:
and paste in the output here... If successful, it should show:
gtsai@<whatever the hostname of 134.79.129.170 is here>
Trying to recreate as closely as possible what knife is actually doing. I suspect this is going to be something silly, but based on your note above about getting logged in manually, this should be working, which is why I want you to attempt that command and paste in the output.
My workstation node is a RHEL7 dhcp-os-129-166
My a-node is a RHEL7: dhcp-os-129-170 , IP=134.179.129.170
On my wokrstation node
[gtsai@dhcp-os-129-166 ~]$ ssh gtsai@134.79.129.170 -i /home/gtsai/.ssh/id_rsa "echo `whoami`@`hostname`"
=>
gtsai@dhcp-os-129-166
(I am still in workstation)
Now from my workstation,
[gtsai@dhcp-os-129-166 ~]$ ssh gtsai@134.79.129.170 -i /home/gtsai/.ssh/id_rsa "
=>
I am in the a-node