examples/vm_power: channel manager and monitor in host

examples/vm_power: channel manager and monitor in host

The manager is responsible for adding communications channels to the Monitor
thread, tracking and reporting VM state and employs the libvirt API for
synchronization with the KVM Hypervisor. The manager interacts with the
Hypervisor to discover the mapping of virtual CPUS(vCPUs) to the host
physical CPUS(pCPUs) and to inspect the VM running state.

The manager provides the following functionality to the CLI:
1) Connect to a libvirtd instance, default: qemu:///system
2) Add a VM to an internal list, each VM is identified by a "name" which must
   correspond a valid libvirt Domain Name.
3) Add communication channels associated with a VM to the epoll based Monitor
   thread.
   The channels must exist and be in the form of:
   /tmp/powermonitor/<vm_name>.<channel_number>. Each channel is a
   Virtio-Serial endpoint configured as an AF_UNIX file socket and opened in
   non-blocking mode.
   Each VM can have a maximum of 64 channels associated with it.
4) Disable or re-enable VM communication channels, channels once added to the
   Monitor thread remain in that threads control, however acting on channel
   requests can be disabled and renabled via CLI.

The monitor is an epoll based infinite loop running in a separate thread that
waits on channel events from VMs and calls the corresponding functions. Channel
definitions from the manager are registered via the epoll event opaque pointer
when calling epoll_ctl(EPOLL_CTL_ADD), this allows for obtaining the channels
file descriptor for reading EPOLLIN events and mapping the vCPU to pCPU(s)
associated with a request from a particular VM.

Signed-off-by: Alan Carew <alan.carew@intel.com>
Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>