Prevent concurrent execution of some tests

when running tests in parallel I had failures on a few tests because they were stepping on each other.

The correct fix would be to change the tests so that they do not clash, but serializing the execution is a valid workaround until somebody wants to correctly tackle the problem.

mentioned in merge request !1732 (merged)

• [2019-03-21 00:10] Validation started with lhcb-tdr-test#489
• [2019-03-22 00:04] Validation started with lhcb-sanitizers#192
• [2019-03-22 00:04] Validation started with lhcb-lcg-dev3#839
• [2019-03-22 00:04] Validation started with lhcb-lcg-dev4#846
• [2019-03-22 00:10] Validation started with lhcb-tdr-test#490
• [2019-03-22 00:10] Validation started with lhcb-head#2182
• [2019-03-22 00:11] Validation started with lhcb-gaudi-head#2196

unmarked as a Work In Progress

removed 1 deleted label

merged

mentioned in commit bd97cfa9

mentioned in commit 0316a242

mentioned in commit f303cdc5

mentioned in commit 1ac41940

mentioned in merge request !1804 (merged)