Glimpse into 2.15-rc1 on CentOS 7

Even if Gerrit 2.15 isn't released yet, it is nice
to give a "glimpse into the future" with a sample
2.15-rc1 docker image to try.

Change-Id: Ic02ecb445b786d178daff3647270786a3e52d47c
diff --git a/centos/7/Dockerfile b/centos/7/Dockerfile
index 56cbd33..a736fdb 100644
--- a/centos/7/Dockerfile
+++ b/centos/7/Dockerfile
@@ -10,7 +10,7 @@
 # Install OpenJDK and Gerrit in two subsequent transactions
 # (pre-trans Gerrit script needs to have access to the Java command)
 RUN yum -y install java-1.8.0-openjdk
-RUN yum -y install gerrit-2.14.3-1
+RUN yum -y install gerrit-2.15.rc1-1
 
 USER gerrit
 RUN java -jar /var/gerrit/bin/gerrit.war init --batch --install-all-plugins -d /var/gerrit