LUCreateInstance: keep src node lock on import
LUCreateInstance: keep src node lock on import

Currently the node lock also guards against removing the import at the
wrong time, so if we're importing an instance image we want to keep the
source node locked. In the future we might want to put export locks at a
different level than node locks.

Reviewed-by: iustinp


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