Update install-imgcrypt to allow change install repo

Add repo env similar to other install script

Signed-off-by: Jing Xu <jinxu@google.com>

script/setup/install-imgcrypt

@@ -23,9 +23,10 @@ set -eu -o pipefail
 script_dir="$(cd -- "$(dirname -- "$0")" > /dev/null 2>&1; pwd -P)"
 
 : "${IMGCRYPT_VERSION:=$(cat "${script_dir}/imgcrypt-version")}"
+: "${IMGCRYPT_REPO:=https://github.com/containerd/imgcrypt.git}" # Default repo
 
 TMPROOT=$(mktemp -d)
-git clone https://github.com/containerd/imgcrypt.git "${TMPROOT}"/imgcrypt
+git clone "${IMGCRYPT_REPO}" "${TMPROOT}"/imgcrypt
 pushd "${TMPROOT}"/imgcrypt
 git checkout "${IMGCRYPT_VERSION}"
 make