In cd93721, I relied on a suprising combination of quotes to protect ssh
execution to strip the quoted path to the private key file.
Since any ssh command line argument can be passed via
`ANSIBLE_SSH_ARGS`, it is quite more readable and easy to rely on the
`-i` argument, which is not affected like `-o IdentityFile=...` and also
supports multiple occurences.
See also http://sourceforge.net/p/fuse/mailman/message/30498048/
Finally fix#6671
Note that I decided to not squash both commits for better
documentation and traceability.
ddbd2a4cfc