Add sudo for RHEL builds

RHEL does not include sudo in the default container image, while other
RPM based distros do.  As a result, some services don't work.  Add
sudo to the base image.

Change-Id: I7014d8cbd90288456e5ab3badcd601ef9cdd0c87
Partially-Implements: blueprint rhel-based-image-support

docker/base/Dockerfile.j2

@@ -148,6 +148,7 @@ RUN yum install -y \
         python-webtest \
         python-werkzeug \
         python-wsme \
+        sudo \
         which \
     && yum clean all
 
@@ -174,6 +175,7 @@ RUN yum update -y \
         python-devel \
         python-oslo-policy \
         sqlite-devel \
+        sudo \
         tar \
         which \
     && yum clean all