Add --repo-only option to configure repositories without installing packages

The `--repo-only` flag allows users to add Docker package repositories
to without automatically installing Docker packages.

This is useful for scenarios where users want to configure the
repository but handle package installation separately.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

Author: vvoland

install.sh

@@ -75,6 +75,14 @@ set -e
 #
 #   $ sudo sh install-docker.sh --mirror AzureChinaCloud
 #
+# --setup-repo
+#
+# Use the --setup-repo option to configure Docker's package repositories without
+# installing Docker packages. This is useful when you want to add the repository
+# but install packages separately:
+#
+#   $ sudo sh install-docker.sh --setup-repo
+#
 # ==============================================================================
 
 
@@ -110,6 +118,7 @@ fi
 
 mirror=''
 DRY_RUN=${DRY_RUN:-}
+REPO_ONLY=${REPO_ONLY:-0}
 while [ $# -gt 0 ]; do
 	case "$1" in
 		--channel)
@@ -127,6 +136,10 @@ while [ $# -gt 0 ]; do
 			VERSION="${2#v}"
 			shift
 			;;
+		--setup-repo)
+			REPO_ONLY=1
+			shift
+			;;
 		--*)
 			echo "Illegal option $1"
 			;;
@@ -519,6 +532,12 @@ do_install() {
 				$sh_c "echo \"$apt_repo\" > /etc/apt/sources.list.d/docker.list"
 				$sh_c 'apt-get -qq update >/dev/null'
 			)
+
+			if [ "$REPO_ONLY" = "1" ]; then
+				echo "Skipping package installation due to --setup-repo flag." >&2
+				exit 0
+			fi
+
 			pkg_version=""
 			if [ -n "$VERSION" ]; then
 				if is_dry_run; then
@@ -608,6 +627,12 @@ do_install() {
 					$sh_c "yum makecache"
 				fi
 			)
+
+			if [ "$REPO_ONLY" = "1" ]; then
+				echo "Skipping package installation due to --setup-repo flag." >&2
+				exit 0
+			fi
+
 			pkg_version=""
 			if command_exists dnf; then
 				pkg_manager="dnf"