Updates to make Zookeeper work (#3424)

Netcat was not included in the centos image.
Also the zookeeper scripts were not executable.
diff --git a/docker/dist/Dockerfile.dist.centos7 b/docker/dist/Dockerfile.dist.centos7
index 88b856c..d19acc7 100644
--- a/docker/dist/Dockerfile.dist.centos7
+++ b/docker/dist/Dockerfile.dist.centos7
@@ -22,6 +22,7 @@
 RUN yum -y install unzip; yum clean all
 RUN yum -y install which; yum clean all
 RUN yum -y install curl; yum clean all
+RUN yum -y install nmap-ncat; yum clean all
 RUN yum -y install python-setuptools; yum clean all
 RUN easy_install supervisor
 RUN echo_supervisord_conf > /etc/supervisord.conf
diff --git a/docker/dist/scripts/generate-zookeeper-config.sh b/docker/dist/scripts/generate-zookeeper-config.sh
old mode 100644
new mode 100755
diff --git a/docker/dist/scripts/install-zookeeper.sh b/docker/dist/scripts/install-zookeeper.sh
old mode 100644
new mode 100755
diff --git a/docker/dist/scripts/start-zookeeper.sh b/docker/dist/scripts/start-zookeeper.sh
old mode 100644
new mode 100755
diff --git a/docker/dist/scripts/wait-for-zookeeper.sh b/docker/dist/scripts/wait-for-zookeeper.sh
old mode 100644
new mode 100755