This patch makes use of the newly added api virConnectListAllDomains()
to list domains in virsh.

Virsh now represents lists of domains using an internal structure
vshDomainList. This structure contains the virDomainPtr list as provided
by virConnectListAllDomains() and the count of domains in the list.

For backwards compatibility, the function vshDomainListCollect was added
that tries to enumerate the domains using the new API and if the API is
not supported falls back to the older approach with the two list
functions.  The helper function also simulates filtering by all
currently supported flags added with virConnectListAllDomains().

This patch also cleans up the "list" command handler to use the new
helpers and adds new command line flags to make use of filtering.