core: preventing NPE on StorageServerConnectionCommandBase

Currently we allow to added FCP connections although they aren't
supported in oVirt - this has been changed by change 2f7c846 as was
required because of how we store the connections password in the DB.
After this change in case of added FCP connection, NPE will occur.
This patch fixes that by restoring the previous state, we may block
adding FCP connections regardless (as having them isn't supported/used
by the engine).

Change-Id: I6662695ba876f9e3f5a22c3251895049bf9eaedc
Signed-off-by: Liron Aravot <laravot@redhat.com>