Modify docker instalation for fedora systems

Use install_package instead of using a specific package manager
while installing docker on fedora systems. With DNF also a
possibility, the better option is to do not take a stand in chosing
which package manager will be used to install packages.

We have a install_package function that will use the appropriate
package manager to install the programs we need to install.

Change-Id: I0524554dae2d6970191ba3afa583480c391b5c3c

devstack/plugin.sh

@@ -956,7 +956,7 @@ function install_docker_ubuntu {
 }
 
 function install_docker_fedora {
-    sudo yum install -y docker
+    install_package docker
     sudo systemctl enable docker
     sudo systemctl start docker
 }