Dan Berrange suggested that using VIR_ENUM_IMPL is more compact
than open-coding switch statements, and still just as forceful
at making us remember to update lists if we add enum values
in the future.  Make this change throughout virsh.

Sure enough, doing this change caught that we missed at least
VIR_STORAGE_VOL_NETDIR.

* tools/virsh-domain-monitor.c (vshDomainIOErrorToString)
(vshDomainControlStateToString, vshDomainStateToString)
(vshDomainStateReasonToString): Change switch to enum lookup.
(cmdDomControl, cmdDominfo): Update caller.
* tools/virsh-domain.c (vshDomainVcpuStateToString)
(vshDomainEventToString, vshDomainEventDetailToString): Change
switch to enum lookup.
(vshDomainBlockJobToString, vshDomainJobToString): New functions.
(cmdVcpuinfo, cmdBlockJob, cmdDomjobinfo, cmdEvent): Update
callers.
* tools/virsh-network.c (vshNetworkEventToString): Change switch
to enum lookup.
* tools/virsh-pool.c (vshStoragePoolStateToString): New function.
(cmdPoolList, cmdPoolInfo): Update callers.
* tools/virsh-volume.c (vshVolumeTypeToString): Change switch to
enum lookup.
(cmdVolInfo, cmdVolList): Update callers.
Signed-off-by: NEric Blake <eblake@redhat.com>