Change all the driver struct initializers to use the
C99 style, leaving out unused fields. This will make
it possible to add new APIs without changing every
driver. eg change:

    qemudDomainResume, /* domainResume */
    qemudDomainShutdown, /* domainShutdown */
    NULL, /* domainReboot */
    qemudDomainDestroy, /* domainDestroy */

to

    .domainResume = qemudDomainResume,
    .domainShutdown = qemudDomainShutdown,
    .domainDestroy = qemudDomainDestroy,

And get rid of any existing C99 style initializersr which
set NULL, eg change

     .listPools          = vboxStorageListPools,
     .numOfDefinedPools  = NULL,
     .listDefinedPools   = NULL,
     .findPoolSources    = NULL,
     .poolLookupByName   = vboxStoragePoolLookupByName,

to

     .listPools          = vboxStorageListPools,
     .poolLookupByName   = vboxStoragePoolLookupByName,