bll: do not allow host activation with no unique id

partial installation of host for various of reasons will leave a host
with no uuid.

these hosts should not be allowed to be activated.

for developers, if the InstallVds option is false, this validation will
be disabled.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=978906
Change-Id: I9a15416ae21c2371ebfb12cecb1551b73c98d88f
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>