Merge pull request #661 from plotly/jun_doc_imagetest

update doc for new testbed setting

Author: etpinard

test/image/README.md

@@ -76,38 +76,12 @@ docker-machine kill default
 
 ### Docker tricks 
 
-##### SSH into docker container
+##### Get into docker container
 
 ```bash
-ssh -p 2022 root@localhost # with password `root`
+docker exec -ti imagetest /bin/bash
 ```
 
-If you got this error:
-
-```
-@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
-@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
-IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
-Someone could be eavesdropping on you right now (man-in-the-middle attack)!
-It is also possible that a host key has just been changed.
-The fingerprint for the ECDSA key sent by the remote host is
-dd:1e:e0:95:8d:ef:06:b8:0f:2f.
-Please contact your system administrator.
-Add correct host key in /home/jh/.ssh/known_hosts to get rid of this message.
-Offending ECDSA key in /home/jh/.ssh/known_hosts:104
-  remove with: ssh-keygen -f "/home/jh/.ssh/known_hosts" -R [localhost]:2022
-ECDSA host key for [localhost]:2022 has changed and you have requested strict checking.
-Host key verification failed.
-```
-simply run
-
-```bash
-ssh-keygen -f "${HOME}/.ssh/known_hosts" -R [localhost]:2022
-```
-
-to remove host information.
-
 ##### List docker machines
 
 ```bash