Add cmdlib tests for removing instance OS params
Add cmdlib tests for removing instance OS params

Add LUInstanceSetParams tests for removing individual public & private
parameters, as well as, for clearing out public & private parameters.

Signed-off-by: Nikos Skalkotos <577541fe0a092079d98e82e6b5d1d5ca8a62ddfb@grnet.gr>
Signed-off-by: Yiannis Tsiouris <471fe235a6f57165a6c832a0b1689a8b8ed2f80e@grnet.gr>
Reviewed-by: Brian Foley <a00e555871a6a538e97f8c44307104c884f8e869@google.com>

yiannist/ganeti,yiannist/ganeti,yiannist/ganeti