xenapi: Resize operations could be faster

 * Improves the code by using only one time resize2fs during the resize.
 * Removes the not used method: "_get_min_sectors".
 * Uses a VDI clone instead of copy in resize_disk's method.
 * Review of some test cases to accept the new behavior
   without _get_min_sectors.

Closes-Bug: 1221332
Change-Id: I40a1d7d467353ba904689d128de7f89d785b4052
Migrate Migration object to Fields

Related to blueprint structured-object-fields

Change-Id: Id09e39f036602116ebdd87f2d063cfff0b3d475d
Migrate SecurityGroup object to Fields

Related to blueprint structured-object-fields

Change-Id: I5f73e403c8adcde4bccc82f35001dbaffe5d3e55
Merge "xenapi: Resize operations could be faster"
Merge "Migrate Migration object to Fields"
Merge "Migrate SecurityGroup object to Fields"
XenAPI: Fix translation of metadetails in aggregates

https://review.openstack.org/#/c/43157/ added a translation from the sqlalchemy model to
the instance object replacing metadetails with metadata.

This added more traces in general for XenAPI (when we queried whether we were using
aggregates) and actually broke the host aggregate functionality

Change-Id: I87195753931945b6e1ecf75bc81575a6fa03068e
Closes-bug: 1232179
xenapi: post install scriptlet to rpm

A freshly installed XenServer requires some modifications in order to be
able to run OpenStack. Nova contains an rpm specification to create a
package with the dom0 plugins, however installing the rpm is not enough.
Some more actions need to be taken:
 - create /images, link to a directory within the local SR
 - setup an ssh keypair, and authenticate it with the host
This change adds a post script to the nova plugins rpm spec file, so
by installing the rpm on a XenServer, it is ready to run OpenStack, no
further manual actions needed.

Change-Id: Id57e3a3ab2782550468c6aa4c01059ceb7cc81ab