Remove flush_operations in the volume usage output

flush_operations is not used by upper layer code and also
according to
ftp://libvirt.org/libvirt/java/javadoc/org/libvirt/DomainBlockStats.html
http://libvirt.org/ruby/api/Libvirt/Domain/BlockStats.html

seems the last value should be errs instead of flush_operations
so remove it from libvirt driver layer.

Change-Id: I438b6fa40e9d97e3ffddda03919c5d577e91c155
Scheduler: return a namedtuple from _get_group_details

Commit 459ca56de2366aea53efc9ad3295fdf4ddcd452c added the utility
method _get_group_details. This patch returns a namedtuple that
contains the hosts and policies for the instance group. This makes
the code easier to read and more robust.

TrivialFix

Change-Id: I76208092b06408022f48b1d965b982af86c78161
Libvirt: Don't let get_console_output crash on missing console file.

During a migration, the console file may be configured, even though
the file itself is not yet present. This patch prevents a
ProcessExecutionError which gets thrown by the chown if the file
doesn't exist.

Change-Id: Ifd75ae911fc264f8284ec3f2adbf1d73bc8c4aca
Related-Bug: #1292339
libvirt: Enable console and log for system z guests

If the host architecture is system z (s390, s390x), the interactive
console and the log of instances will be defined as "console" devices
(instead of "serial" devices) in libvirts domain XML. These console
devices need to have a "target type". For the interactive console this
is "sclp" and for the log "sclplm".

Partial-Implements blueprint libvirt-kvm-systemz

Change-Id: I20d5e32fee660e77c52b6fc5fdf1128a996bb994
Merge "Scheduler: return a namedtuple from _get_group_details"
Merge "Remove flush_operations in the volume usage output"
Merge "Libvirt: Don't let get_console_output crash on missing console file."
Merge "libvirt: Enable console and log for system z guests"