New APIs for checking some object properties

New APIs for checking some object properties

Introduce a number of new APIs to  expose some boolean properties
of objects, which cannot otherwise reliably determined, nor are
aspects of the XML configuration.

 * virDomainIsActive: Checking virDomainGetID is not reliable
   since it is not possible to distinguish between error condition
   and inactive domain for ID of -1.
 * virDomainIsPersistent: Check whether a persistent config exists
   for the domain

 * virNetworkIsActive: Check whether the network is active
 * virNetworkIsPersistent: Check whether a persistent config exists
   for the network

 * virStoragePoolIsActive: Check whether the storage pool is active
 * virStoragePoolIsPersistent: Check whether a persistent config exists
   for the storage pool

 * virInterfaceIsActive: Check whether the host interface is active

 * virConnectIsSecure: whether the communication channel to the
   hypervisor is secure
 * virConnectIsEncrypted: whether any network based commnunication
   channels are encrypted

NB, a channel can be secure, even if not encrypted, eg if it does
not involve the network, like a UNIX socket, or pipe.

 * include/libvirt/libvirt.h.in: Define public API
 * src/driver.h: Define internal driver API
 * src/libvirt.c: Implement public API entry point
 * src/libvirt_public.syms: Export API symbols
 * src/esx/esx_driver.c, src/lxc/lxc_driver.c,
   src/interface/netcf_driver.c, src/network/bridge_driver.c,
   src/opennebula/one_driver.c, src/openvz/openvz_driver.c,
   src/phyp/phyp_driver.c, src/qemu/qemu_driver.c,
   src/remote/remote_driver.c, src/test/test_driver.c,
   src/uml/uml_driver.c, src/vbox/vbox_tmpl.c,
   src/xen/xen_driver.c: Stub out driver tables