Ambari Cluster Provisioning Failure -- No More Mirrors To Try

Saw this when trying to re-provision a cluster after doing an "ambari-server reset" (Ambari 1.6.1 on Redhat 6.5):

Fail: Execution of '/usr/bin/yum -d 0 -e 0 -y install hadoop-yarn' returned 1. Error Downloading Packages:

  hadoop-yarn-2.4.0.2.1.5.0-695.el6.x86_64: failure: hadoop/hadoop-yarn-2.4.0.2.1.5.0-695.el6.x86_64.rpm from HDP-2.1: [Errno 256] No more mirrors to try.

  hadoop-2.4.0.2.1.5.0-695.el6.x86_64: failure: hadoop/hadoop-2.4.0.2.1.5.0-695.el6.x86_64.rpm from HDP-2.1: [Errno 256] No more mirrors to try.

  zookeeper-3.4.5.2.1.5.0-695.el6.noarch: failure: zookeeper/zookeeper-3.4.5.2.1.5.0-695.el6.noarch.rpm from HDP-2.1: [Errno 256] No more mirrors to try.

The solution was to do a "yum clean all" on the agents and retrying (requires doing all the "ambari-server reset" and agent cleanup again).