Fixed migration destination prep regression

By adding set_instance_params(), which is used both by
normal instance startup code and migration destination
prep code, fixed the regression introduced while fixing
EUCA-5837

Fixes EUCA-5882
Merge remote-tracking branch 'origin/dev/dmitrii/EUCA-5882' into dev/juphoff/evac-test
[CC] Generate/use 16-alphanum-character pseudorandom shared secret for migrations
     (rather than timestamp).

Implements EUCA-5097.
Merge remote-tracking branch 'origin/testing' into dev/juphoff/evac-test
Merge remote-tracking branch 'origin/dev/juphoff/evac-test' into testing