util: reject unknown flags, and prefer unsigned flags

util: reject unknown flags, and prefer unsigned flags

Silently ignored flags get in the way of new features that
use those flags.  Also, an upcoming syntax check will favor
unsigned flags.

* src/nodeinfo.h (nodeGetCPUStats, nodeGetMemoryStats): Drop
unused attribute.
* src/interface/netcf_driver.c (interfaceOpenInterface)
(interfaceDefineXML, interfaceCreate, interfaceDestroy): Reject
unknown flags.
* src/network/bridge_driver.c (networkOpenNetwork)
(networkGetXMLDesc): Likewise.
* src/nwfilter/nwfilter_driver.c (nwfilterOpen): Likewise.
* src/secret/secret_driver.c (secretOpen, secretDefineXML)
(secretGetXMLDesc, secretSetValue): Likewise.
* src/util/logging.c (virLogDefineFilter, virLogDefineOutput)
(virLogMessage): Likewise; also use unsigned flags.
* src/util/logging.h (virLogDefineFilter, virLogDefineOutput)
(virLogMessage): Change signature.
* src/util/command.c (virExecWithHook): Likewise.