RHV: Cannot upgrade SHE from 3.6 to 4.0: ovirt-ha-agent is still active

Issue

• Cannot proceed with the upgrade of Self Hosted Engine from RHV 3.6 to 4.0

2018-10-11 17:45:26 WARNING otopi.plugins.gr_he_upgradeappliance.core.misc misc._validata_lm_volumes:316 ovirt-ha-agent is still active on host host.example.com, please stop it (it can require a few seconds).
2018-10-11 17:45:27 DEBUG otopi.context context._executeMethod:142 method exception
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/otopi/context.py", line 132, in _executeMethod
    method['method']()
  File "/usr/share/ovirt-hosted-engine-setup/scripts/../plugins/gr-he-upgradeappliance/core/misc.py", line 319, in _validata_lm_volumes
    time.sleep(2)
  File "/usr/lib/python2.7/site-packages/otopi/main.py", line 53, in _signal
    raise RuntimeError("SIG%s" % signum)
RuntimeError: SIG2