docker: Add a glib2-2.22 image

It's a variation of our existing centos6, plus two more lines to
downgrade glib2 to version 2.22 which we download from vault.centos.org.

Suggested-by: Paolo Bonzini <pbonzoni@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Message-Id: <1470708908-12885-1-git-send-email-famz@redhat.com>

tests/docker/dockerfiles/min-glib.docker

@@ -0,0 +1,8 @@
+FROM centos:6
+RUN yum install -y \
+    tar git make gcc g++ \
+    zlib-devel SDL-devel pixman-devel \
+    epel-release
+RUN yum install -y libfdt-devel ccache
+RUN yum downgrade -y http://vault.centos.org/6.0/os/x86_64/Packages/glib2-2.22.5-5.el6.x86_64.rpm
+RUN yum install -y http://vault.centos.org/6.0/os/x86_64/Packages/glib2-devel-2.22.5-5.el6.x86_64.rpm