Avoid saam to declare global mountpoints not matching its configuration

Test Plan

• saam

diff origin/production/saam.internal.softwareheritage.org current/saam.internal.softwareheritage.org
*******************************************
- Exec[create /tmp]
*******************************************
- File[/tmp]
*******************************************
- Mount[/tmp]
*******************************************
- Mount[swap]
*******************************************
*** End octocatalog-diff on saam.internal.softwareheritage.org

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Migrated from D7081 (view on Phabricator)