Ensure rbd connect exception is properly caught

If the rbd driver fails to connect to Ceph the exception
was not being properly caught resulting in the volume
remaining in the 'creating' state until the corresponding
task eventually times out (on top of the time it took
for the connect to fail).

Also added config option for rados connect timeout.

Conflicts:
    cinder/volume/drivers/rbd.py
    etc/cinder/cinder.conf.sample

DocImpact: new config option 'rados_connect_timout'
(cherry picked from commit 02e4afbd8108ca26af09ccaebb8b1c8b72ea3f3f)
Change-Id: I5e6eaaaf6bed3e139ff476ecf9510ebe214a83f9
Eventlet green threads not released back to pool

Presently, the wsgi server allows persist connections hence even after
the response is sent to the client, it doesn't close the client socket
connection.
Because of this problem, the green thread is not released back to the pool.

In order to close the client socket connection explicitly after the
response is sent and read successfully by the client, you simply have to
set keepalive to False when you create a wsgi server.

DocImpact:
Added wsgi_keep_alive option (default=True).
In order to maintain the backward compatibility, setting wsgi_keep_alive
as True by default. Recommended is set it to False.

Conflicts:
        cinder/wsgi.py
        etc/cinder/cinder.conf.sample

SecurityImpact

Closes-Bug: #1361360
Change-Id: Ic57b2aceb136e8626388cfe4df72b2f47cb0661c
(cherry picked from commit fc87da7eeb3451e139ee71b31095d0b9093332ce)
Merge "Ensure rbd connect exception is properly caught" into stable/icehouse
Merge "Eventlet green threads not released back to pool" into stable/icehouse