Qemu Session Support

[qazokm]

Added basic qemu support in response to issue #272. The patch supports creating storage pools under user directories and using existing networks created under the qemu:///system connection. Using existing networks requires the qemu-bridge-helper to be installed and the relevant permissions granted (this is the default on some distros but others may need to configure this).

To assist with this the following configuration options where added

• qemu_use_session
  • Enable usage of qemu session, changes default connection URL to qemu:///session and enables support for qemu session
• storage_pool_path
  • Storage pool path to use for libvirt images
  • Defaults to /var/lib/libvirt/images
  • If session enabled defaults to ~/.local/share/libvirt/images)
• management_network_device
  • Device to use for management network
  • Defaults to 'virbr0'
• system_uri
  • QEMU system URL to connect to as read-only to retrieve DHCP leases for obtaining IP addresses

[pronix]

hello @qazokm
thanks for huge impact. it will take time for testing.
can you also add some information to README, for example same as in description.
thank you

[qazokm]

No problem, added a basic example with links to QEMU bridge helper information

[pronix]

@qazokm thank you. check please some changes 99371fe

[little-dude]

Thanks a lot for this @qazokm. It would be nice to have a release with this.

[voxik]

@qazokm nice work 👍 but have you considered to submit part of your changes to fog-libvirt? E.g. default_storage_volume.xml.erb would not be needed here if the owner and group tags were supported by fog-libvirt and on the first look, it just looks it would be just a minor change.