Race condition:
User calls defineXML to create new instance.
The main thread from vzDomainDefineXMLFlags() creates new instance by prlsdkCreateVm.
Then this thread calls prlsdkAddDomain to add new domain to domains list.
The second thread receives notification from hypervisor that new VM was created.
It calls prlsdkHandleVmAddedEvent() and also tries to add new domain to domains list.
These two threads call virDomainObjListFindByUUID() from prlsdkAddDomain() and don't find new domain.
So they add two domains with the same uuid to domains list.

This fix splits logic of prlsdkAddDomain() into two functions.
1. vzNewDomain() creates new empty domain in domains list with the specific uuid.
2. prlsdkLoadDomain() add data from VM to domain object.

New algorithm for creating an instance:
In vzDomainDefineXMLFlags() we add new domain to domain list by calling vzNewDomain()
and only after that we call CreateVm() to create VM.
It means that we "reserve" domain object with the specific uuid.
After creation of new VM we add info from this VM
to reserved domain object by calling prlsdkLoadDomain().

Before this patch prlsdkLoadDomain() worked in 2 different cases:
1. It creates and initializes new domain. Then updates it from sdk handle.
2. It updates existed domain from sdk handle.
In this patch we remove code which creates new domain from LoadDomain()
and move it to vzNewDomain().
Now prlsdkLoadDomain() only updates domain from skd handle.

In notification handler prlsdkHandleVmAddedEvent() we check
the existence of a domain and if it doesn't exist we add new domain by calling
vzNewDomain() and load info from sdk handle via prlsdkLoadDomain().