Allow to specify storage policy when uploading objects

Client already supports -H/--header option when creating container
or uploading objects. This patch extends this option to support
Storage Policy.

e.g.,
    swift post con -H 'X-Storage-Policy:p1'
This creates one container 'con' with storage policy 'p1'.

    swift upload con obj -H 'X-Storage-Policy:p2'
This creates container 'con' with storage policy 'p2' and uploads
object 'obj' into it.

Also fixes segmented uploading to non-default storage policy container

When uploading large objects with segmentation to container with
non-default storage policy, there will be another 'xxx_segments'
container created, but with the default storage policy. This
results all the segments to be stored with the wrong policy.

This patch is for the Storage Policy feature, and also
compatible with old versions w/o Storage Policy support.

Change-Id: I5c19e90604a0bcf2c85e1732b8a0b97ae6801994
Merge "Allow to specify storage policy when uploading objects"
Fix context sensitive help for info and tempurl

Make it so that swift <cmd> --help will print the info
subcommand help for info and tempurl just like all the
other subcommands.

Also add unit tests to verify subcommand help.

Change-Id: Id3666dcf72a9727fbfda2f74c23293ada1c53aa0
Add importable SwiftService incorporating shell.py logic

This patch adds a SwiftService class that incorporates the high
level logic from swiftclient/shell.py. It also ports shell.py to
use the new class, and updates the code in swiftclient/multithreading.py
to allow the SwiftService to be used for multiple operations whilst
using only one thread pool.

Change-Id: I08c5796b4c01001d79fd571651c3017c16462ffd
Implements: blueprint bin-swift-logic-as-importable-library