Add Ignore path-specification to codenvy/che-mount utility

[TylerJewell]

This adds a capability to the codenvy/che-mount utility that improves synchronization performance by allowing users of the utility to provide a unison profile that contains matching files, directories along with patterns that can be ignored. By ignoring large directories or certain patterns, the synchronization can be improved performance-wise.

Please note - the syntax has been modified. It is no longer necessary to volume mount the .ssh directory. To provide a unison profile, create a file named default.prf. You can provide any valid unison profile for this, which include name patterns, regex. You then need to mount the directory where this file resides to /profile in the container.

Docs on Profiles
Docs on Ignore

TODO - Che CLI will need to be updated to remove the .ssh mount and to also provide this file as a hard coded file. Perhaps we have people place it in ~/.che/unison/default.prf. We will always expect it there, if it is provided at all.

Usage on Linux 
  docker run --rm -it --cap-add SYS_ADMIN --device /dev/fuse
            --name che-mount
            -v /etc/group:/etc/group:ro 
            -v /etc/passwd:/etc/passwd:ro 
            -v <path-to-sync-profile>:/profile
            -u \$(id -u \${USER})
            -v <local-mount>/:/mnthost codenvy/che-mount <ip> <port> 

Usage on Mac or Windows:
  docker run --rm -it --cap-add SYS_ADMIN --device /dev/fuse
            --name che-mount 
            -v <path-to-sync-profile>:/profile
            -v <local-mount>/:/mnthost codenvy/che-mount <ip> <port>

     <local-mount>    Host directory to sync files, must end with a slash '/'
     <ip>             IP address of Che server
     <port>           Port of workspace SSH server - retrieve inside workspace

To build this container for usage now, you can:

git clone http://github.com/eclipse/che-dockerfiles
cd che-dockerfiles
git checkout add-ignore-mount
cd che-mount
docker build -t codenvy/che-mount:nightly .

[TylerJewell]

@benoitf