I created this plist in ~/Library/LaunchAgents after install RabbitMQ via Homebrew.

com.rabbitmq.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
        "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Label</key>
        <string>com.rabbitmq</string>
        <key>Program</key>
        <string>/usr/local/sbin/rabbitmq-server</string>
        <key>RunAtLoad</key>
        <true/>
        <key>UserName</key>
        <string>your-username-here!</string>
        <!-- need erl in the path -->
        <key>EnvironmentVariables</key>
        <dict>
          <key>PATH</key>
          <string>/usr/local/sbin:/usr/bin:/bin:/usr/local/bin</string>
        </dict>
</dict>
</plist>