Need set compute driver's flag capabilities correctly

[ChangBo Guo(gcb)]

1.Back ground:
Class ComputeDriver, base of all compute drivers, has dictionary capabilities
to indicate if the compute driver implements some functions. The 'supports_recreate'
flag needs the driver to support the evacuate operation. The 'has_imagecache' flag
needs the driver to implement the 'manage_image_cache' method.[1] Compute manger will
check this with capabilities['has_imagecache'] [2]or capabilities['supports_recreate']
[3]directly.

2. Problems:
1)Docker does not currently support these two functions, so the capabilities flags
should not be set.[4]
2)Baremetal only set 'has_imagecache', there is code path leading KeyError.
Need set capabilities explicitly to avoid this.[5]

3.Solution:
Set or unset compute driver's capabilities explicitly.

[1] https://github.com/openstack/nova/blob/master/nova/virt/driver.py#L128
[2] https://github.com/openstack/nova/blob/master/nova/compute/manager.py#L5168
[3] https://github.com/openstack/nova/blob/master/nova/compute/manager.py#L2142
[4] https://github.com/openstack/nova/blob/master/nova/virt/docker/driver.py#L62
[5] https://github.com/openstack/nova/blob/master/nova/virt/baremetal/driver.py#L114

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/59258
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=6a932aebbc68989485d4867920a6a6bbf536f6c6
Submitter: Jenkins
Branch: master

commit 6a932aebbc68989485d4867920a6a6bbf536f6c6
Author: Chang Bo Guo <email address hidden>
Date: Sat Nov 30 01:04:06 2013 -0800

    Remove docker's unsupported capabilities

    The 'supports_recreate' flag needs the driver to support the evacuate
    operation. The 'has_imagecache' flag needs the driver to implement the
    'manage_image_cache' method. Docker does not currently support these
    two functions, so the capabilities flags should not be set.

    Partial-Bug: #1261636

    Change-Id: I191d0d8cd35aece52462c0477f2d89897bb762c1