extend logging to record configuration-related changes

extend logging to record configuration-related changes

Currently libvirt's default logging is limited and it is difficult to
determine what was happening when a proglem occurred (especially on a
machines where one don't know the detail.)  This patch helps to do that
by making additional logging available for the following events:

  creating/defining/undefining domains
  creating/defining/undefining/starting/stopping networks
  creating/defining/undefining/starting/stopping storage pools
  creating/defining/undefining/starting/stopping storage volumes.

* AUTHORS: add Naoya Horiguchi
* src/network/bridge_driver.c src/qemu/qemu_driver.c
  src/storage/storage_driver.c: provide more VIR_INFO logging