[core] rename VdsStatic hostname to hostName.

Change field name to match setters and getters.

in UpdateVdsCommand changed attribute names are derived
from  getters/setters while the list of changeable fields
are derived from the field name (see vdsHandler.Init())

Change-Id: Ie6461e1ed17506f7ea2a8897ad2a3847d466268f
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1003282
Signed-off-by: Mooli Tayer <mtayer@redhat.com>