Now that the openstack resource provider allocation unset command is
available [1] this change adds a note about using it in the troubleshooting
doc for cleaning up orphaned allocations.
Sub-sections are used to try and separate the two non-heal_allocations
solutions with the recommended solution first (using the new unset command).
While in here I noticed a typo in the heal_allocations section as well and
fixed it.
[1] I627bfd1ff699d075028da6afafbe7fb9b2f13058
Change-Id: I896bb68c4bdd35d051ef3e95e19bdeb472f9bc99
Related-Bug: #1829479
6c704cc1c5