Use correct object when deleting

SwiftSignalHandle was using the client object instead
of the client plugin object to check for Not Found
during delete. Also normalized access to the client
and plugin as well as remove a few pep8 warning items.

Change-Id: Ib73cb3846feb6ccb2e45859458008a1701aa2231
Closes-Bug: #1382226
Merge "Use correct object when deleting"