Fixes to {I,}HiveWhiteBoard

Follow up on !388 (merged):

• restore use of recursive_mutex (required to avoid a deadlock in MiniBrunel)
• Add method to IHiveWhiteBoard to explicitly register new items (will be needed by FetchDataFromFile)
• remove unused IHiveWiteBoard::newDataObjectsPresent()
• avoid OUT parameters & StatusCode, prefer to just return the OUT parameter
• fix comments

@sponce: FYI, this mr fixes a deadlock in MiniBrunel introduced in !388 (merged) -- should have stayed with the recursive mutex...

approved this merge request

• [2017-10-12 00:06] Validation started with lhcb-future-clang#340
• [2017-10-12 00:08] Validation started with lhcb-future#564
• [2017-10-13 00:17] Validation started with lhcb-future-clang#341
• [2017-10-13 00:17] Validation started with lhcb-future#565
• [2017-10-14 00:03] Validation started with lhcb-future#566
• [2017-10-14 00:04] Validation started with lhcb-future-clang#342
• [2017-10-15 00:02] Validation started with lhcb-future-clang#343
• [2017-10-15 00:02] Validation started with lhcb-future#567
• [2017-10-16 00:03] Validation started with lhcb-future-clang#344
• [2017-10-16 00:03] Validation started with lhcb-future#568
• [2017-10-17 00:03] Validation started with lhcb-future#569
• [2017-10-17 00:04] Validation started with lhcb-future-clang#345
• [2017-10-18 00:04] Validation started with lhcb-future#570
• [2017-10-18 00:04] Validation started with lhcb-future-clang#346
• [2017-10-19 00:02] Validation started with lhcb-future#571
• [2017-10-19 00:03] Validation started with lhcb-future-clang#347

added 1 commit

• a0ef7a15 - Follow up on !388 (merged)

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resolved all discussions

changed the description

added 1 commit

• 5356da65 - update gitlab-ci.yml to use centos7

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added 6 commits

• 5356da65...4ab7848b - 4 commits from branch gaudi:master
• 8f5dba81 - update gitlab-ci.yml to use centos7
• 719580b1 - Follow up on !388 (merged)

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factored out the update of gitlab-ci into !433 (merged), and re-based this mr on top of !433 (merged)

added 3 commits

• 549a50b0 - Fixed the version of clang-format
• c9fb6678 - Do not install argparse, not needed on CentOS7 (Python 2.7)
• 13d92ed4 - Follow up on !388 (merged)

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@graven thanks for the info, you've just saved my afternoon, as I read it less than 2h before hitting the issue !

added 2 commits

• be604bd8 - apply python formatting rules
• 8d4e4050 - Follow up on !388 (merged)

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added 1 commit

• 4b1fda73 - Follow up on !388 (merged)

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added 5 commits

• 4b1fda73...6395abfb - 4 commits from branch gaudi:master
• f0eb780d - Follow up on !388 (merged)

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changed milestone to %v30r0

added C++ framework label

added backport to v29 label

removed backport to v29 label

added 14 commits

• f0eb780d...a69472d5 - 13 commits from branch gaudi:master
• f7db4d6a - Follow up on !388 (merged)

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