virsh: Allow using VIR_AUTOPTR for releasing virDomainPtr in virsh

virsh: Allow using VIR_AUTOPTR for releasing virDomainPtr in virsh

I opted to alias the 'virDomainType' to 'virshDomain' so that it's
obvious in all cases that this is a virsh-only construct. This is also
somewhat consistent with virsh's use of 'virshDomainFree' wrapper for
the freeing function which actually accepts NULL.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>