Bug fixes after work on BM16
BLISS installation on BM16 (with Staffan and Mauro Rovezzi) helped showing bugs affecting virtual axes when several BLISS instances are running at the same time (like, Tango servers upon BLISS and a BLISS command line).
Merge requests !569 (merged), !570 (merged) and !571 (merged) fix the problems and provide tests for continuous integration.