Che CLI: added some parameters to execute che-mount

[l0rd]

What does this PR do?

Adapt Che CLI to the che-mount updates introduced by eclipse-che/che-dockerfiles#18:

• Fix local synched folder permissions on Linux
• Persist workspace SSH ECDSA key fingerprint in local ~/.ssh/known_hosts

What issues does this PR fix or reference?

• Improvements to che-mount che-dockerfiles#18

[codenvy-ci]

Can one of the admins verify this patch?

[benoitf]

how to provide custom ssh key if it's not stored in user home folder ?

for example with che dir up, ssh files are stored in the .che directory
is that an option to provide private key is possible ?

for example sshfs option seems to be
-o IdentityFile=/path/to/key

[l0rd]

@benoitf This PR do not address that. Using option IdentityFile would be a way to do that or we can just run che-mount using volume -v /path/to/key:${HOME}/.ssh/key