Set the volume access mode during volume attach

cinderclient supports an optional keyword argument named 'mode'
for volumes.attach(), which allows you to set the access mode of
a volume at attach time. The keyword argument is not passed in
by nova when it attaches a read-only volume, making the volume
access mode default to 'rw' instead of the desired 'ro'. This
patch finds the access mode of the volume and passes it to
cinderclient, so the correct access mode is used at attach
time.

Change-Id: Ib62f454292e60114f96debbad96c4a356dc32a21
Closes-Bug: #1307088
remove unneeded call to network_api on detach_interface

When detaching an interface from an instance we call the network_api
which results in calling neutron and updating the info cache. We do not
actually need to do this as we can get the nw_info directly from the
instance's info cache which removes the call to neutron.

Closes-bug: 1294886

Change-Id: Ifbfff958146a4a01b2d9c656180ef4a95e154312
Merge "remove unneeded call to network_api on detach_interface"
Merge "Set the volume access mode during volume attach"