Add a type class for the property of being forthcoming
Add a type class for the property of being forthcoming

This type class captures those objects where it is meaningful
to ask if the object presented to us is forthcoming.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Petr Pudlak <9d19625f8ee825a2c398462ed335cbcf98f79c32@google.com>

leshchevds/ganeti,yiannist/ganeti,bitemyapp/ganeti,andir/ganeti,yiannist/ganeti,grnet/snf-ganeti,leshchevds/ganeti,ganeti/ganeti,mbakke/ganeti,onponomarev/ganeti,andir/ganeti,yiannist/ganeti,dimara/ganeti,dimara/ganeti,mbakke/ganeti,grnet/snf-ganeti,mbakke/ganeti,onponomarev/ganeti,ganeti/ganeti,leshchevds/ganeti,apyrgio/ganeti,andir/ganeti,bitemyapp/ganeti,ganeti/ganeti,apyrgio/ganeti