stricter check during image selection

    if istools.isfile(name) and os.path.isfile(name):

        return PackageImage(name), None

    else:

        (repo, image, version) = re.match("((\w+)/)?(\w+)(:v?(\d+))?", name).group(2,3,5)

        x = re.match("^((\w+)/)?(\w+)(:v?(\d+))?$", name)

        if x is None:

            raise Exception("%s is not a valid image" % name)

        (repo, image, version) = x.group(2,3,5)

        debug("Selected image is %s v%s in %s" % (image, version, repo))

        if repo is None:

            return repoman.get(image, version)

        else:

        # is no version take the last

        if version is None:

            version = self.last(name)

            if version < 0:

                raise Exception("Unable to find last version of %s in %s" % (name,

                                                                             self.config.name))

        # get file md5 from db

        r = self.db.ask("select md5 from image where name = ? and version = ? limit 1",

                        (name,version)).fetchone()