Configurable docker yum repos, systemd fix

* Make yum repos used for installing docker rpms configurable
* TasksMax is only supported in systemd version >= 226
* Change to systemd file should restart docker

roles/docker/templates/docker.service.j2

@@ -24,7 +24,9 @@ ExecStart={{ docker_bin_dir }}/docker daemon \
           $DOCKER_NETWORK_OPTIONS \
           $DOCKER_DNS_OPTIONS \
           $INSECURE_REGISTRY
+{% if systemd_version.stdout|int >= 226 %}
 TasksMax=infinity
+{% endif %}
 LimitNOFILE=1048576
 LimitNPROC=1048576
 LimitCORE=infinity

roles/docker/templates/rh_docker.repo.j2

@@ -1,7 +1,7 @@
 [dockerrepo]
 name=Docker Repository
-baseurl=https://yum.dockerproject.org/repo/main/centos/7
+baseurl={{ docker_rh_repo_base_url }}
 enabled=1
 gpgcheck=1
-gpgkey=https://yum.dockerproject.org/gpg
+gpgkey={{ docker_rh_repo_gpgkey }}
 {% if http_proxy is defined %}proxy={{ http_proxy }}{% endif %}