"puppet facts upload" face only tries first master in server_list

Puppet Version: 5.5.1
Puppet Server Version: 5.5.2 (2018.1.0.41)
OS Name/Version: RHEL 7

When a node's puppet.conf specifies multiple masters in server_list the facts upload face only tries the first master in the list. If this fails due to a hostname lookup failure on the first master the face exits with an error, rather than trying the second master.

Steps to reproduce:

• remove any "server" configs from puppet.conf
• add the following "server_list" configuration: "foo.example,actual-master.example" (where "actual-master.example" is the working master address, and "foo.example" is not resolvable to an IP address)
• run "puppet facts upload"

Desired Behavior:

• the face should gracefully fail over to the second master in the server_list and complete the facts upload successfully

Actual Behavior:

• the face fails with the following error message:

# puppet facts upload

Notice: Uploading facts for 'pe-201730-master.puppetdebug.vlan' to: 'foo.example'

Error: Failed to open TCP connection to foo.example:8140 (getaddrinfo: Name or service not known)

Error: Try 'puppet help facts upload' for usage

I'm attaching the output of "puppet facts upload --debug --trace" as well.

This face (and the facts endpoint in puppetserver) were (re)added in this PR: https://github.com/puppetlabs/puppet/pull/6434