ci: Fix FIH Docker image release usage

The scripts for fih tests install and run where running different
versions of the docker images, since the install specified a version and
not version was specified for run, defaulting to `latest`.

This commits adds a new file for specifying the docker image to be used.

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/ci/fih-tests_install.sh b/ci/fih-tests_install.sh
index d69308a..1e78aaf 100755
--- a/ci/fih-tests_install.sh
+++ b/ci/fih-tests_install.sh
@@ -16,9 +16,11 @@
 
 set -e
 
+source $(dirname "$0")/fih-tests_version.sh
+
 DOCKER_DIR=docker
 
-IMAGE=fih-test:0.0.2
+IMAGE=fih-test:$FIH_IMAGE_VERSION
 
 CACHED_IMAGE=$DOCKER_DIR/$IMAGE