Upload abortion is now detected within the  OC_Connector_Sabre_File::put()

OC_Connector_Sabre_AbortedUploadDetectionPlugin is pointless

Adding unit test testUploadAbort()

Backport of ea269f0 from master
Merge pull request #9523 from owncloud/stable6-fix-9302-master

[stable6] Upload abortion is now detected within the  OC_Connector_Sabre_File::put...