ec2-infra: ping after wait_for_connection

Got a (strange) error during provisioning for one of the host:

TASK [wait for linux host to be available] *************************************
Tuesday 13 March 2018  10:07:46 -0400 (0:00:00.128)       0:03:21.596 *********
ok: [ec2-18-232-187-2.compute-1.amazonaws.com]
ok: [ec2-35-171-244-244.compute-1.amazonaws.com]
ok: [ec2-18-232-38-165.compute-1.amazonaws.com]
ok: [ec2-18-232-198-104.compute-1.amazonaws.com]
ok: [ec2-18-232-8-218.compute-1.amazonaws.com]
ok: [ec2-18-232-31-98.compute-1.amazonaws.com]
ok: [ec2-35-174-101-190.compute-1.amazonaws.com]

TASK [Set hostname based on tag_internaldns] ***********************************
Tuesday 13 March 2018  10:10:08 -0400 (0:02:21.396)       0:05:42.993 *********
fatal: [ec2-18-232-187-2.compute-1.amazonaws.com]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Stdio forwarding request failed: Session open refused by peer\r\nssh_exchange_identification: Connection closed by remote host\r\n", "unreachable": true}
changed: [ec2-35-174-101-190.compute-1.amazonaws.com]
changed: [ec2-18-232-8-218.compute-1.amazonaws.com]
changed: [ec2-35-171-244-244.compute-1.amazonaws.com]
changed: [ec2-18-232-38-165.compute-1.amazonaws.com]
changed: [ec2-18-232-198-104.compute-1.amazonaws.com]
changed: [ec2-18-232-31-98.compute-1.amazonaws.com]

Try to fix this by retrying a couple of times right after wait_for_connection.