[ci] integration: "Install" netcat if needed (#2161)

We recently updated our Buildkite stack. The new version of the agents
doesn't come with netcat installed, which we use in our integration
tests. "Install" it if necessary.

scripts/docker-integration-tests/run.sh

@@ -17,6 +17,29 @@ TESTS=(
 	scripts/docker-integration-tests/coordinator_config_rules/test.sh
 )
 
+# Some systems, including our default Buildkite hosts, don't come with netcat
+# installed and we may not have perms to install it. "Install" it in the worst
+# possible way.
+if ! command -v nc && [[ "$BUILDKITE" == "true" ]]; then
+	echo "installing netcat"
+	NCDIR="$(mktemp -d)"
+
+	yumdownloader --destdir "$NCDIR" --resolve nc
+	(
+		cd "$NCDIR"
+		RPM=$(find . -maxdepth 1 -name '*.rpm' | tail -n1)
+		rpm2cpio "$RPM" | cpio -id
+	)
+
+	export PATH="$PATH:$NCDIR/usr/bin"
+
+	function cleanup_nc() {
+		rm -rf "$NCDIR"
+	}
+
+	trap cleanup_nc EXIT
+fi
+
 scripts/docker-integration-tests/setup.sh
 
 NUM_TESTS=${#TESTS[@]}