qemumonitorjsontest: Refactor chardev hotplug testing

qemumonitorjsontest: Refactor chardev hotplug testing

The main objective of this patch is to use a proper instance of
virDomainChrSourceDef allocated with the private data.

To achieve this the test cases are grouped into blocks by how much they
fill in the chardev definition. Some test cases are moved around so
that the resulting sequence doesn't need extra clearing.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>