Code review comment for lp://staging/~nuclearbob/utah/bug1147306

Note that for provisioned machines only "install-deb-command.jinja2" is used to
install the client package and that the "add_backslash" filter is only used by
"utah-latecommand-in-target.jinja2". Hence, lines 20-25 in the diff can be removed
since they aren't needed.

We could also have a new module that takes care of the template environment to
avoid the duplication of the filter code, but for now I think that probably
that's an overkill unless we find a case in which the filter code duplication
is really needed.

By the way, for all the other machines there shouldn't be any problem since
ProvisionedMachine is the only machine class that doesn't call the
Machine.__init__ method through chained super calls. In the future, it would be
nice to have a class hierarchy in which the initialization method is reused for
all subclasses.

I need to add provisioned machines to the set of basic tests that I run for
each change to make sure things aren't broken like in this case.