Export DOCKER_GRAPHDRIVER and DOCKER_EXECDRIVER in integration-cli

This needed for our "small" testing daemon using same config as "big"
testing daemon.

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

project/make/.integration-daemon-start

@@ -12,8 +12,8 @@ fi
 # intentionally open a couple bogus file descriptors to help test that they get scrubbed in containers
 exec 41>&1 42>&2
 
-DOCKER_GRAPHDRIVER=${DOCKER_GRAPHDRIVER:-vfs}
-DOCKER_EXECDRIVER=${DOCKER_EXECDRIVER:-native}
+export DOCKER_GRAPHDRIVER=${DOCKER_GRAPHDRIVER:-vfs}
+export DOCKER_EXECDRIVER=${DOCKER_EXECDRIVER:-native}
 
 if [ -z "$DOCKER_TEST_HOST" ]; then
 	( set -x; exec \