Clarify Confluence Data Center upgrade documentation

Step 5 on https://confluence.atlassian.com/display/DOC/Upgrading+Confluence+Data+Center says:

Step 5 Upgrade the other nodes

To upgrade the next node in your cluster:

1. Stop Confluence on the first node.
2. Copy the installation directory and home directory from the first node to the next node.
   If the path to the local home directory is different on this node, edit the confluence-init.properties to point to the correct location.
3. Start Confluence, and and confirm that you can log in and view pages before continuing with the next node.
   Repeat this process for each remaining node.

The steps are correct, but the header is slightly misleading. We should clarify that after upgrading one node, the other nodes are not upgraded but rather replicated from the single upgraded node. Users should not attempt to upgrade the other nodes like they did for the first node, since all nodes share the same DB, which would have already been upgraded.

For sub-step 5.2 I would also recommend to add "local" to the home directory in the first sentence, i.e.:

Copy the installation directory and local home directory from the first node to the next node.