Verify configuration version number before parsing
Verify configuration version number before parsing

As the attempt to convert the dict used as json representation
of the configuration into a configuration object already makes
assumptions about the internal representation, verify the version
before such an attempt. Fixes issue 783.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>

yiannist/ganeti,grnet/snf-ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,yiannist/ganeti,onponomarev/ganeti,grnet/snf-ganeti,yiannist/ganeti,andir/ganeti,dimara/ganeti,dimara/ganeti,onponomarev/ganeti,ganeti/ganeti,apyrgio/snf-ganeti,mbakke/ganeti,mbakke/ganeti,bitemyapp/ganeti,mbakke/ganeti,apyrgio/ganeti,bitemyapp/ganeti,ganeti/ganeti,leshchevds/ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/snf-ganeti,andir/ganeti,ganeti/ganeti,apyrgio/ganeti,andir/ganeti