Set a sane default for state_path

This change sets a sane default to state_path and puts the previous
state_path for tests only.

Because the default value of state_path changed, if this one isn't set in the
configuration file, pybasedir is not more used as replacement but /var/lib/nova
is used instead.

UpgradeImpact
DocImpact
Closes bug: #1240879

Change-Id: I94502bcfac8b372271acd0dbc1710c0e3009b8e1
Make image props filter handle old vm_modes

The ImagePropertyFilter would fail to build an instance if the image
used an older style vm_mode (e.g. 'pv') as described in
nova.compute.vm_mode.  This change will convert the vm mode string to
the current form.

Change-Id: Ibde37e28b02d9e866b286ea14c47a6a8411d94b4
Closes-Bug: #1276773
Move policy check of start/stop to api layer

This patch moves "compute:start/stop" to api layer for ec2 and nova
v2 api, and uses "compute:v3:servers:start/stop" for nova api v3.
Also removes policy check from compute api. And give default rules
for v3 policy check.

Add core_authorizer with 'compute:' as the scope of core api in v3.
That's for distinguishing core and extension api. Use different namespace
for policy. The policy of core api will be 'compute:v3:extension_name'.

Partially implements bp v3-api-policy
DocImpact

Change-Id: I6c4f1c677b64015c61440f9db941d1ab9cf77b48
Merge "Move policy check of start/stop to api layer"
Merge "Set a sane default for state_path"
Merge "Make image props filter handle old vm_modes"
Merge commit 'refs/changes/97/66597/4' of git://gold.eng.hq.xensource.com/git/github/openstack/nova into tmpbranch