Fix verify config if a node has no instances
Fix verify config if a node has no instances

Do not try to provide a fake instance UUID called "no instances", as
trying to get the name for would fail and raise an exception.

Signed-off-by: Thomas Thrainer <98bdeac947eb8ca18146e9ce7f092788ec242cd1@google.com>
Reviewed-by: Michele Tartara <05f7077a2c6cbbdc4af4ba42e3ef89a0df846179@google.com>

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