Support outdating a config
Support outdating a config

The config reader has a cached copy of the configuration.
Support marking it as outdated. In that way, we will later
be able to restrict reads to the case if we don't have
an up-to-date copy.

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

Cherry-picked from 1ee7c1e2a31276113eee062b42cae54ccd4de578

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

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