updated dependencies
addressed issue https://github.com/globaleaks/GlobaLeaks/issues/828
minor UT fix
minor fix in order to address https://github.com/globaleaks/GlobaLeaks/issues/828
Catch exceptions more strictly.

Make sure that the key file name does not exist already.
addressed issue https://github.com/globaleaks/GlobaLeaks/issues/831
Use uuid module for generating uuid4