arm arch: 1. install required libraries; 2. umount /proc after dockerfs.

Author: taocy

files/build_templates/sonic_debian_extension.j2

@@ -268,6 +268,8 @@ sudo LANG=C chroot $FILESYSTEM_ROOT systemctl disable core_uploader.service
 sudo cp $IMAGE_CONFIGS/corefile_uploader/core_uploader.py $FILESYSTEM_ROOT/usr/bin/
 sudo cp $IMAGE_CONFIGS/corefile_uploader/core_analyzer.rc.json $FILESYSTEM_ROOT_ETC_SONIC/
 sudo chmod og-rw $FILESYSTEM_ROOT_ETC_SONIC/core_analyzer.rc.json
+
+sudo LANG=C DEBIAN_FRONTEND=noninteractive chroot $FILESYSTEM_ROOT apt-get -y install libffi-dev libssl-dev
 sudo https_proxy=$https_proxy LANG=C chroot $FILESYSTEM_ROOT pip install azure-storage==0.36.0
 sudo https_proxy=$https_proxy LANG=C chroot $FILESYSTEM_ROOT pip install watchdog==0.10.2
 sudo https_proxy=$https_proxy LANG=C chroot $FILESYSTEM_ROOT pip install futures==3.3.0
@@ -461,14 +463,14 @@ echo "docker images pull complete"
 
 sudo umount $FILESYSTEM_ROOT/target
 sudo rm -r $FILESYSTEM_ROOT/target
-sudo umount /proc || true
 if [[ $CONFIGURED_ARCH == armhf || $CONFIGURED_ARCH == arm64 ]]; then
     sudo umount $FILESYSTEM_ROOT/dockerfs
     sudo rm -fr $FILESYSTEM_ROOT/dockerfs
     sudo kill -9 `sudo $SONIC_NATIVE_DOCKERD_FOR_DOCKERFS_PID` || true
 else
     sudo chroot $FILESYSTEM_ROOT service docker stop
 fi
+sudo umount /proc || true
 sudo rm $FILESYSTEM_ROOT/etc/init.d/docker
 {% for script in installer_start_scripts.split(' ') -%}
 sudo cp {{script}} $FILESYSTEM_ROOT/usr/bin/