sharedfs: skip hypervisors without system templates

[Dogface2k]

Fixes #13825

Summary

Prevent CreateSharedFileSystem from dereferencing a missing system VM template when a zone contains mixed hypervisor types.

Root cause

deploySharedFSVM() shuffles the supported hypervisors. When a hypervisor has no ready system VM template and another hypervisor remains, the existing null check fell through to template.getId() instead of trying the next hypervisor. This caused the reported intermittent NPE for mixed zones such as VMware plus External/MaaS.

Fix

Skip hypervisors without a ready system VM template while alternatives remain. Preserve the existing explicit CloudRuntimeException when the final candidate also has no template.

Validation

• Reproduced the issue twice on the live CloudStack installation using an enabled, hostless External cluster alongside VMware; the exact template is null NPE occurred on the External-first attempt.
• Removed all temporary clusters and test resources after reproduction; the zone returned to its original VMware-only state.
• The focused regression test fails on the unfixed 4.22 branch with the exact NPE.
• The focused Maven reactor test passes after the fix: 10 tests, 0 failures, 0 errors.

Scope

This is limited to SharedFS hypervisor template selection and its regression test. No UI, API contract, database schema, or deployment behavior is changed.

[DaanHoogland]

clgtm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 17.69%. Comparing base (5328528) to head (a42798a).

Additional details and impacted files

@@             Coverage Diff              @@
##               4.22   #13830      +/-   ##
============================================
- Coverage     17.69%   17.69%   -0.01%     
  Complexity    15835    15835              
============================================
  Files          5925     5925              
  Lines        533539   533541       +2     
  Branches      65274    65275       +1     
============================================
- Hits          94427    94424       -3     
- Misses       428435   428442       +7     
+ Partials      10677    10675       -2     

Flag	Coverage Δ
uitests	3.69% <ø> (ø)
unittests	18.77% <100.00%> (-0.01%)	⬇️

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[DaanHoogland]

@blueorangutan package