Improvement: Filesystem permission check

##### ISSUE TYPE
* Improvement Request

##### COMPONENT NAME

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cloudstack-sysvmadm
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##### CLOUDSTACK VERSION
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N/A
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##### CONFIGURATION

N/A

##### OS / ENVIRONMENT
Cloudstack running on linux systems

##### SUMMARY
Check filesystem permission before upgrading systemvms

##### STEPS TO REPRODUCE

Currently, when issuing the cloudstack-sysvmadm script for upgrading the systemvms (or doing it manually), the process starts without any prechecks.
When there is somehow an issue with filesystem permissions, the new systemvm.iso cannot be copied to the new location. It would be a nice enhancement, when cloudstack had a health check or at least the cloudstack-sysvmadm script a permission check.

A newly introduced health check could continuously check some relevant cloudstack metrics, including the filesystem permissions and show a simple go/nogo somewhere in the admin ui. Or the simple way: a script or the modified sysvmadm script which checks first all storage paths for the correct rights.

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##### EXPECTED RESULTS

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##### ACTUAL RESULTS

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Comienza localizando el punto de entrada cloudstack-sysvmadm y cómo descubre las rutas de almacenamiento antes de actualizar las System VMs. Revisa el flujo de actualización existente y determina las comprobaciones de permisos esperadas y el comportamiento ante fallos. Se considera completado cuando el script o health check elegido detecta permisos inutilizables antes de que comience la copia o la actualización de systemvm.iso.

Escrito por el modelo de indexación a partir del texto del issue.