fvp-docker-images/builders.sh: Run "df -h" before building each image

To check free disk space.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I04ac2bae6637c76de46501df685a6ac39f63211c
diff --git a/fvp-docker-images/builders.sh b/fvp-docker-images/builders.sh
index a3210b5..8ba3714 100644
--- a/fvp-docker-images/builders.sh
+++ b/fvp-docker-images/builders.sh
@@ -24,6 +24,7 @@
 
 for tarball in F*.tgz
 do
+    df -h
     tag=$(./create-model-tag.sh $tarball)
     mkdir -p $tag
     cp setup-sshd stdout-flush-wrapper*.sh $tag/