Add tests for bin/swift

Tests are written to ensure bin/swift is working properly and using
functions from swiftclient modules as expected.

Change-Id: Idb0581516b7e0a41c97977bb0bb9f8290f67ad13
Makes use of requests.Session

This allows better connection pooling and may improve performances.

Change-Id: I69e986b7387dd3ac281731b8355a3eec34a537f8
Merge "Add tests for bin/swift"
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