On Debian 9, 'pbuilder create' fails because of lack of GPG key for 3rdparty repo, so we need --allow-untrusted on 'pbuilder create' and 'pbuilder update'. Also, apt-key adv --fetch-keys does not works correctly on it, but we can use "curl <URL> | apt-key add -" as workaround. Fixes #3088 Signed-off-by: Takuya ASADA <syuu@scylladb.com> Message-Id: <1513797714-18067-1-git-send-email-syuu@scylladb.com>