Improvements to path handling

[lucaspar]

SFDS-177

Gateway

• Bugfix: Disconnecting older files from existing captures on update (bug caught by added integration tests on the SDK side).
• Capture top-level directory is now normalized on creation and updates.
• Removed the need to specify an absolute path.
  • As a result, the File post serializer now uses a common sanitization function for the path.
• Moved factory-boy to base requirements to run tests in QA.

SDK

• New tests to cover regressions of different kinds of path usage.
• Bugfix: File.local_path attribute was not being set for some downloads.
• Improved test for client.capture.read test: now it checks the number of files associated to the capture.
• Better control over logging messages: client's verbose flag propagates to submodules and sub-APIs.