Add a helper to connect to Xpra inside the Docker container

Images generated by 'docker commit' actually do not inherit the CMD.
Therefore, when we try to commit the public key into the image, we will
lose the default command.

We could now play nasty little sed games with the output of 'docker
inspect', but the better way is to use a shared directory (useful for
data exchange in any case) for the container to pick up the public key:
that way, the image will actually not contain any default public key
(and can therefore not be forgotten to be replaced).

We will keep the change here, however, for the historical record.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add the placeholder directory shared/

With the upcoming change to connect.sh, we will map said directory
automatically into the Docker image (as /shared/).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Use a better way to get authorized_keys installed

The previous attempt to commit the public ssh key into the image was
misguided: it asked for over-sharing of information.

Instead, let's just pick up the public key from the shared/ directory and
install it into $HOME/.ssh/authorized_keys upon container startup (via
docker-desktop).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
connect.sh: do not complain about unknown host key

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Get rid of startup.sh

We really can do almost all of it in the Dockerfile. The only thing we cannot do there is the password generation; The plan is to move away from the password anyway, in favor of a to-be-generated private/public key pair.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Switch to a seamless desktop

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Start the Xpra server when starting the container

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Start ssh daemon first and keep Xpra in the foreground

That way, if Xpra stops running, the container stops running, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Upgrade to saucy

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Avoid dpkg-divert hack

Apparently, it is no longer necessary now that we are starting dbus
correctly.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Adjust README

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Pick up all id_*.pub keys in shared/

Some people might want to connect to their Xpra instance from multiple
accounts; Best practices dictate that multiple accounts should have
multiple private ssh keys, so we allow that by installing all public
ssh keys dropped into shared/id_*.pub into the authorized_keys file.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>