parallels: don't add domain to the list twice

parallels: don't add domain to the list twice

There is a problem with function parallelsDomainDefineXML. If we
are defining a new domain, then we need to do 2 things: aclually
create a VM in PCS and add new domain to the cached list of domains
_parallelsConn.domains.

This is done in the function parallelsLoadDomains. So call to
virDomainObjListAdd will return a error, because a domain
with the same name and id will already be in the list.

Signed-off-by: Dmitry Guryanov <dguryanov@parallels.com>