Description of problem:
Given a host that is HE deployed AND running the HE vm
When an attempt to put the host to maintenance is made
Then the host does NOT move to maintenance and the migration fails due to a libvirt error:

 2018-10-29 11:09:14,917+0200 ERROR (migsrc/22a15a5c) [virt.vm] (vmId='22a15a5c-0f21-4979-a0bc-963d2af4b7ad') Failed to migrate (migration:455)
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/vdsm/virt/migration.py", line 437, in _regular_run
    self._startUnderlyingMigration(time.time())
  File "/usr/lib/python2.7/site-packages/vdsm/virt/migration.py", line 509, in _startUnderlyingMigration
    self._perform_with_conv_schedule(duri, muri)
  File "/usr/lib/python2.7/site-packages/vdsm/virt/migration.py", line 587, in _perform_with_conv_schedule
    self._perform_migration(duri, muri)
  File "/usr/lib/python2.7/site-packages/vdsm/virt/migration.py", line 529, in _perform_migration
    self._migration_flags)
  File "/usr/lib/python2.7/site-packages/vdsm/virt/virdomain.py", line 98, in f
    ret = attr(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/vdsm/common/libvirtconnection.py", line 130, in wrapper
    ret = f(*args, **kwargs)
  File "/usr/lib/python2.7/site-packages/vdsm/common/function.py", line 92, in wrapper
    return func(inst, *args, **kwargs)
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 1779, in migrateToURI3
    if ret == -1: raise libvirtError ('virDomainMigrateToURI3() failed', dom=self)
libvirtError: Unsafe migration: Migration without shared storage is unsafe 

=================================================================
This bug is similar to: https://bugzilla.redhat.com/show_bug.cgi?id=1635621
Which was reported to happen over shared storage of Gluster type, however
this time the shared storage was NFS.
=================================================================

Version-Release number of selected component (if applicable):
Ovirt engine 4.2.7.4-0.1.el7ev
vdsm-4.20.43-1.el7ev.x86_64
libvirt-4.5.0-10.el7_6.2.x86_64

How reproducible:
Reproduces in Automation only (100%)

Steps to Reproduce:
1. Put a host that the HE vm resides on to maintenance.

Actual results:
Maintenance fails because the migration of the HE vm fails.

Expected results:
The host should be in maintenance mode and the HE vm should be migrated successfully to another host in the cluster.

Additional info:
1. The hosted storage was of NFS type.
2. The source host was host_mixed_1 and the target host was host_mixed_3.
3. The Traceback mentioned earlier occurs on the source host, while on the 
   target host there is no error of such kind.