packaging: Add get_last_modification()

Let's add a function to get the hash of the last commit modifying a
specific file.

This will help to avoid writing `git rev-list ...` into every single
build script used by the kata-deploy.

Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>

tools/packaging/scripts/lib.sh

@@ -113,4 +113,19 @@ get_config_version() {
 	else
 		die "failed to find ${config_version_file}"
 	fi
-}
+}
+
+# $1 - Repo's root dir
+# $2 - The file we're looking for the last modification
+get_last_modification() {
+	local repo_root_dir="${1}"
+	local file="${2}"
+
+	# This is a workaround needed for when running this code on Jenkins
+	git config --global --add safe.directory ${repo_root_dir} &> /dev/null
+
+	dirty=""
+	[ $(git status --porcelain | grep "${file}" | wc -l) -gt 0 ] && dirty="-dirty"
+
+	echo "$(git log -1 --pretty=format:"%H" ${file})${dirty}"
+}