build_container: Install rsync in image

`rsync` is required for installing kernel headers, which will be used in
`seccompiler` crate to generate syscall tables.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

Author: RuoqingHe

build_container.sh

@@ -8,7 +8,7 @@ apt-get update
 
 # DEBIAN_FRONTEND is set for tzdata.
 DEBIAN_FRONTEND="noninteractive" apt-get install --no-install-recommends -y \
-    curl gcc musl-tools git python3 python3-pip shellcheck \
+    curl gcc musl-tools git python3 python3-pip shellcheck rsync \
     libssl-dev tzdata cmake g++ pkg-config jq libcurl4-openssl-dev libelf-dev \
     libdw-dev binutils-dev libiberty-dev make \
     cpio bc flex bison wget xz-utils fakeroot \