Add a few predefined variables to CI builds

This adds CI_BUILD_TAG, CI_BUILD_STAGE, CI_BUILD_NAME and CI_BUILD_TRIGGERED to build environment.

This change is based on: !1530 (merged)

This resolves #2769 (closed)

Please review

/cc @dzaporozhets @vsizov

mentioned in issue #2769 (closed)

Added 3 commits:

• daca1c65 - Fix broken tests
• 766da5fa - Fix broken matrix_for_ref?
• c778951b - Added CI_BUILD_TAG, _STAGE, _NAME and _TRIGGERED to CI builds

Added 2 commits:

• 4bf69b0b - Fix feature tests
• d13ee71e - Added CI_BUILD_TAG, _STAGE, _NAME and _TRIGGERED to CI builds

Added 31 commits:

• d13ee71e...e3edd53a - 30 commits from branch master
• 1a6e7d3a - Added CI_BUILD_TAG, _STAGE, _NAME and _TRIGGERED to CI builds

Added 1 commit:

• 07c98710 - Use tag? instead of tag to indicate that this is boolean

Added 20 commits:

• 07c98710...82da19ce - 18 commits from branch master
• 585be53d - Added CI_BUILD_TAG, _STAGE, _NAME and _TRIGGERED to CI builds
• 9212d7a6 - Use tag? instead of tag to indicate that this is boolean

Looks good to me

Added 7 commits:

• 9212d7a6...3b93d37e - 5 commits from branch master
• 0cd8e64f - Added CI_BUILD_TAG, _STAGE, _NAME and _TRIGGERED to CI builds
• fcc6338a - Use tag? instead of tag to indicate that this is boolean

Added 5 commits:

• fcc6338a...2d0fcb4d - 3 commits from branch master
• 7b5ab3de - Added CI_BUILD_TAG, _STAGE, _NAME and _TRIGGERED to CI builds
• 58074195 - Use tag? instead of tag to indicate that this is boolean

Status changed to merged

mentioned in commit 45c0b74d