qemu_domain: Avoid using qemuDomainObjPrivatePtr as parameter

qemu_domain: Avoid using qemuDomainObjPrivatePtr as parameter

In functions `qemuDomainObjInitJob`, `qemuDomainObjResetJob`,
`qemuDomainObjResetAgentJob`, `qemuDomainObjResetAsyncJob`,
`qemuDomainObjFreeJob`, `qemuDomainJobAllowed`,
`qemuDomainNestedJobAllowed` we avoid sending the complete
qemuDomainObjPrivatePtr as parameter and instead just send
qemuDomainJobObjPtr.

This is done in a effort to separating the qemu-job APIs into
a spearate file.

Signed-off-by: Prathamesh Chavan <pc44800@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>