rhui-installer fails with 'FileNotFoundError: [Errno 2] No such file or directory'

Issue

rhui-installer fails with 'FileNotFoundError: [Errno 2] No such file or directory'
I'm running 'rhui-installer' command as root user, but the error seems to refer to '/home/test-user/.ssh/authorized_keys'.

# rhui-installer --cds-lb-hostname=cds-lb.example.com --rhua-hostname=rhua.example.com --remote-fs-type=nfs --remote-fs-server=nfs.example.com:/export
                /root/.ssh/id_rsa_rhua Already exists
Traceback (most recent call last):
  File "/usr/bin/rhui-installer", line 11, in <module>
    load_entry_point('rhui-installer==4.4.0', 'console_scripts', 'rhui-installer')()
  File "/usr/lib/python3.6/site-packages/rhui/rhui_installer.py", line 218, in main
    RhuaInstaller().install()
  File "/usr/lib/python3.6/site-packages/rhui/rhui_installer.py", line 66, in install
    self.gen_ssh_keys()
  File "/usr/lib/python3.6/site-packages/rhui/rhui_installer.py", line 160, in gen_ssh_keys
    append_file(SSH_KEYFILE + '.pub', self.user_ssh_auth_keys)
  File "/usr/lib/python3.6/site-packages/rhui/utils.py", line 21, in append_file
    with open(dst_file, 'a') as f:
FileNotFoundError: [Errno 2] No such file or directory: '/home/test-user/.ssh/authorized_keys'