Description of problem:
The upgrade of satellite 6.3 is impossible, when yum-cache directory is mounted directly

Version-Release number of selected component (if applicable):
rubygem-foreman_maintain-0.1.5-1.el7sat.noarch

How reproducible:
always

Steps to Reproduce:
1. mount /dev/sdb /var/cache/yum
2. # foreman-maintain upgrade run --target-version 6.3


Actual results:
Running Migration scripts to Satellite 6.3
================================================================================
Setup repositories:
| Configuring repositories for 6.3                                    [OK]
--------------------------------------------------------------------------------
Update package(s) :
Loaded plugins: enabled_repos_upload, package_upload, product-id, search-disabled-repos, subscription-manager
Cleaning repos: rhel-7-server-rpms rhel-7-server-satellite-6.3-rpms
              : rhel-7-server-satellite-maintenance-6-rpms rhel-7-server-satellite-tools-6.3-rpms
              : rhel-server-rhscl-7-rpms
Cleaning up everything
Maybe you want: rm -rf /var/cache/yum, to also free up space taken by orphaned data from disabled or removed                       repos
Uploading Enabled Repositories Report
Loaded plugins: product-id, subscription-manager
                                                                      [FAIL]
Failed executing rm -rf /var/cache/yum, exit status 1:
rm: cannot remove ‘/var/cache/yum’: Device or resource busy
--------------------------------------------------------------------------------
Scenario [Migration scripts to Satellite 6.3] failed.
 
The following steps ended up in failing state:
 
  [packages-update]

Expected results:
No error


Additional info:

Changing the rb-file workaround this issue

/usr/share/gems/gems/foreman_maintain-0.1.5/lib/foreman_maintain/concerns/system_helpers.rb

...
- 109         execute!('rm -rf /var/cache/yum')
+ 109         execute!('rm -rf /var/cache/yum/*')
...

==> adding '/*' at the end of the command