remote: dispatch: Allocate 'virDomainDef' in ACL helpers dynamically

remote: dispatch: Allocate 'virDomainDef' in ACL helpers dynamically

At time of this patch struct 'virDomainDef' has 1736 bytes. Allocate it
dynamically to keep the stack frame size in reasonable values.

This patch also fixes remoteRelayDomainQemuMonitorEventCheckACL, where
we didn't clear the stack'd variable prior to use. Fortunately for now
the code didn't look at anything else than what the code overwrote.

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