Handle checkout failure for unbuilt elements

Description

Trying to checkout an element that has not been build yet (that has no artefact cached yet) leads to a BUG + stack trace.

Changes proposed in this merge request:

• Raise an ElementError in Element.stage_artifact() if the element has not yet produced an artifact, as suggested by the doctring.
• Advise on running bst build first as details of the raise exception.
• Ensure that the exception is caught and that the advice reached the caller.

This merge request, when approved, will close issue/bug: #447 (closed)

I have checked this out and verifies that it behaviours as described.

approved this merge request

approved this merge request

approved this merge request

added 17 commits

• 2ec2f82e...4fc1f5d1 - 15 commits from branch master
• acf0112e - element.py: Raise an exception on unbuilt element checkout
• de3c11e4 - _stream.py: Print details on checkout failure

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enabled an automatic merge when the pipeline for de3c11e4 succeeds

canceled the automatic merge

added 8 commits

• de3c11e4...480565c2 - 6 commits from branch master
• f91799e6 - element.py: Raise an exception on unbuilt element checkout
• 18aa78ba - _stream.py: Print details on checkout failure

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enabled an automatic merge when the pipeline for 18aa78ba succeeds

added 2 commits

• c7657763 - element.py: Raise an exception on unbuilt element checkout
• ebe57d20 - _stream.py: Print details on checkout failure

Compare with previous version

enabled an automatic merge when the pipeline for ebe57d20 succeeds

added 4 commits

• ebe57d20...d10e4668 - 2 commits from branch master
• 425f3b87 - element.py: Raise an exception on unbuilt element checkout
• b254ba71 - _stream.py: Print details on checkout failure

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added 18 commits

• b254ba71...eabc3899 - 16 commits from branch master
• a0ab6b56 - element.py: Raise an exception on unbuilt element checkout
• 79db4bf5 - _stream.py: Print details on checkout failure

Compare with previous version

added 5 commits

• 79db4bf5...62a250fe - 3 commits from branch master
• 00ddcbd7 - element.py: Raise an exception on unbuilt element checkout
• 4c739e2a - _stream.py: Print details on checkout failure

Compare with previous version

merged

mentioned in commit 4a4fed7a

mentioned in merge request !653 (merged)