This adds a new method, Capabilities(), which returns an XML
definition of the hypervisor's system capabilities, much like
`virsh capabilities`.
I've only included integration tests for these two methods due to the
large amount of data returned by the capabilities call.
This adds support for dumping a domain's XML definition, akin to `virsh
dumpxml <domain>`. The returned data is quite large so I've included an
integration test rather than adding a huge blob of hex to `libvirttest`.
This modifies the travis-ci configuration to build and install libvirt
1.2.2 and 2.3.0 for integration testing. Simple integration tests have
been included for Connect() and Disconnect().
