Before this change, the detection of a non-existing path on the guest
machine was considered as an error and lead to interrupt the current vagrant
action. This was actually a mistake to do so, since the config checks
are performed before many other vagrant actions than `provision`.
The config.validate phase is also intended to primarily check the options
sanity, but it cannot be too strict with the guest state (which can easily
get "out of automatic control").
With this change, we still apply these checks (when possible), but only warn
about possible configuration problems. This way, the subsequent
statements will happen anyway (e.g. ansible commands will be
executed, vagrant machine will be destroyed, etc.)
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.
Surprisingly (to me at least), a simple quote enclosure was not enough
to fix the problem.
Caveat: the stringified ansible-playbook command logged in verbose mode
is wrongly formatted (no quotes are escaped).
Fix#6671