ARROW-8107: [Packaging][APT] Use HTTPS for LLVM APT repository for De…

…bian GNU/Linux stretch

Closes #6607 from kou/packaging-apt-stretch-https

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

dev/tasks/linux-packages/apache-arrow/apt/debian-stretch/Dockerfile

@@ -35,10 +35,11 @@ RUN \
   quiet=$([ "${DEBUG}" = "yes" ] || echo "-qq") && \
   apt update ${quiet} && \
   apt install -y -V ${quiet} \
+    apt-transport-https \
     gnupg \
     wget && \
   wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add - && \
-  echo "deb http://apt.llvm.org/stretch/ llvm-toolchain-stretch-7 main" > \
+  echo "deb https://apt.llvm.org/stretch/ llvm-toolchain-stretch-7 main" > \
     /etc/apt/sources.list.d/llvm.list && \
   apt update ${quiet} && \
   apt install -y -V ${quiet} \