Cannot find a valid baseurl for repo: centos-openstack-train/7/x86_64'

[centos-openstack-train]
name=CentOS-7 - OpenStack train
baseurl=https://mirrors.aliyun.com/centos/7/cloud/x86_64/openstack-train#####注释原有源，添加该行
#baseurl=http://mirror.centos.org/$contentdir/$releasever/cloud/$basearch/openstack-train/
#mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=cloud-openstack-train
gpgcheck=0
enabled=1
exclude=sip,PyQt4