storage: validate NFS secondary storage mount using SSVM during image store discovery

[SURYAS1306]

###Description

This PR addresses issue #12674 where CloudStack allows adding a secondary storage (image store) even when the provided NFS mount path is invalid.

Currently during image store discovery, CloudStack persists the image store in the database without validating whether the Secondary Storage VM (SSVM) can access the NFS export.
The failure only appears later during system VM template seeding (setup-sysvm-tmplt), producing errors in logs while the API/UI reports successful storage addition.

This leads to an inconsistent state where unusable secondary storage is registered in the system.

Previously validation occurred only during System VM template seeding; this change introduces fail-fast validation during image store discovery.

This PR performs immediate validation using SSVM during image store discovery:

• During discovery, the management server sends a setup command (generateSetupCommand) to an available SSVM in the same zone to verify the storage can be prepared/mounted.

• If the SSVM setup command fails:

  • the created image store is rolled back
  • a CloudRuntimeException is thrown
  • the API returns failure instead of success

This prevents unusable secondary storage from being registered and avoids late failures during system VM template registration.

Fixes: #12674

---

Types of changes

• Breaking change
• New feature
• Bug fix
• Enhancement
• Cleanup
• Build/CI
• Test

---

Bug Severity

• BLOCKER
• Critical
• Major
• Minor
• Trivial

---

How Has This Been Tested?

Environment

• Apache CloudStack 4.22
• KVM hypervisor
• NFS secondary storage

Test Scenarios

1. Valid NFS mount

   • Secondary storage added successfully
   • SSVM mount successful
   • Templates seeded correctly

2. Invalid NFS mount

   • API returns error
   • Image store not persisted in database
   • No template seeding attempted

3. Regression check

   • Primary storage behavior unchanged
   • Existing valid secondary storages unaffected

Unit tests executed:

mvn -pl server -Dtest=StorageManagerImplTest,SecondaryStorageManagerImplTest test

---

How did you try to break this feature and the system with this change?

• Wrong NFS export path
• Non-exported directory
• Unreachable NFS server IP

In all cases, storage creation failed correctly and no invalid store was registered.

[shwstppr]

Will need validation for a new zone

[Copilot]

Pull request overview

This PR aims to prevent registering unusable NFS secondary storage by performing fail-fast validation during image store discovery, using a Secondary Storage VM (SSVM) to verify the mount before proceeding.

Changes:

• Injects SecondaryStorageVmManager into StorageManagerImpl.
• Adds SSVM-based validation logic inside discoverImageStore and rolls back the image store on validation failure.
• Returns an error to the API caller when SSVM setup/mount validation fails.

---

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 53 lines in your changes missing coverage. Please review.
✅ Project coverage is 17.60%. Comparing base (5caf6cd) to head (174b37d).

Files with missing lines	Patch %	Lines
...ain/java/com/cloud/storage/StorageManagerImpl.java	0.00%	53 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               4.22   #12678      +/-   ##
============================================
- Coverage     17.60%   17.60%   -0.01%     
- Complexity    15659    15660       +1     
============================================
  Files          5917     5917              
  Lines        531394   531447      +53     
  Branches      64970    64977       +7     
============================================
- Hits          93575    93563      -12     
- Misses       427269   427335      +66     
+ Partials      10550    10549       -1     

Flag	Coverage Δ
uitests	3.70% <ø> (ø)
unittests	18.67% <0.00%> (-0.01%)	⬇️

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