Fix test_multipass_copy

The chunk size was set on the wrong driver (source instead of
target). The size of the transfer has been reduced to 100 bytes
instead of 100KB in order to have a much faster test.
Improve test_rules stability

A different was used each time, but the old files were not
deleted. Now the two reps are created before each test.
Use last version of Logbook instead of Onitu's fork
Improve error handling in LocalStorage. Fix #23

Catch errors when calling stat. Except both IOError and OSError in
all clauses.
Add Python 3.4 to tox and Travis
Add custom exceptions in the Plug
Handle exceptions in the Dealer. Fix #24
Use the new exceptions in Local Storage
Update the docs with the new exceptions
Merge branch '#24_handlers_exceptions' into develop
Amazon S3 Driver : Proof of Concept
* Rollback to the real Proof of Concept original version instead of the broken multipart one
* Modification to pass flake8 build