Improve error messages when vdi_type is missing

[klmp200]

Explicit error message pointing to missing vdi_type on SRMetadata update Add a distinction for unpacking corrupted empty metadata headers for easier diagnostic

[MarkSymsCtx]

These changes are probably fine but currently fail on coverage grounds

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Diff Coverage
Diff: github/master...HEAD, staged and unstaged changes
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libs/sm/drivers/LVHDSR.py (66.7%): Missing lines 244
libs/sm/srmetadata.py (50.0%): Missing lines 183,186-187
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Total:   9 lines
Missing: 4 lines
Coverage: 55%
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Please add suitable unit tests to exercise this functionality to ensure that it remain functional going forward. More than 80% coverage of new code will be required and where possible full coverage of code and important conditions.

[klmp200]

These changes are probably fine but currently fail on coverage grounds

-------------
Diff Coverage
Diff: github/master...HEAD, staged and unstaged changes
-------------
libs/sm/drivers/LVHDSR.py (66.7%): Missing lines 244
libs/sm/srmetadata.py (50.0%): Missing lines 183,186-187
-------------
Total:   9 lines
Missing: 4 lines
Coverage: 55%
-------------

Please add suitable unit tests to exercise this functionality to ensure that it remain functional going forward. More than 80% coverage of new code will be required and where possible full coverage of code and important conditions.

You're right, I should have done it in the first place.
It's all good now :)