Make --tenant a required arg for quota-show

Previously, novaclient was incorrectly defaulting to the tenant name
as the tenant ID when retrieving quota thresholds via the os-quota-sets
API extension, in an apparent attempt to default to the current tenant
if no specific tenant is explicitly requested.

As a result, the default quotas were always returned, regardless of
whether there were specific overridden quotas for this tenant.

We now require that the --tenant option is always specified for the
quota-show verb, as a sensible default isn't always possible
(because the tenant ID may be opaque to the client, for example when
the auth token is cached in the keyring from a previous call out to
keystone - now the tenant ID is of course generally embedded in the
nova publicURL retrieved from the service catalog, but that is not
guaranteed to be the case, i.e. I don't think we can safely make
assumptions about that URL format).

This change also makes the quota-show verb more consistent with the
quota-update verb, which currently requires that the tenant is
always explicitly specified.

Fixes rhbz: 888697
Upstream change: https://review.openstack.org/18412
Change-Id: I1706ad993059e70ca0e2f3bcf7b1d06cbcc39f2d
cherry-picked: e6e22dbe77cbcb9e2078ab8574ebb75575ab2168
Fix the help text of add-fixed-ip

Makes the help text of the add-fixed-ip less confusing by pointing out
that the IP address is taken from the given network and assigned to the
server.

Fixes rhbz: 890966
Upstream change: https://review.openstack.org/18963
Change-Id: Iaf4641f65a5872ee70273d5b972ff5da0ddd7b1d
cherry-picked: 2d3e0d949e5d2b63c13a0f82b0ab2b4227a5a3e1
Mask permissions on private key files

When using "nova x509-create-cert", the private key should be written to
a file with the permissions 0400, not (world-readable) 0644, in line
with how ssh private keys are treated.

Fixes rhbz: 905075
Upstream change: https://review.openstack.org/21007
Change-Id: I0b20378efba38fa58f4ad9a33cd15b3432ebb8a2
cherry-picked: 0b4590cb2438b4ec1fd8842d7ae3f2627059cabc