cli: do not show db errors

[diegodelemos]

Currently, if there is something wrong with the database, either a connection problem or a query problem, we show the psycop2 stack trace which always leaks information (DB username, table and field names...). We should give more user-friendly and secure errors.

$ # edit R-DB deployment to use a different password (it is set as env variable)
$ # this will redeploy R-DB with a password different to the one loaded in RS and RWC
$ reana-client run
[INFO] Creating a workflow...
Cannot create workflow : 
(psycopg2.OperationalError) FATAL:  password authentication failed for user "reana"

(Background on this error at: http://sqlalche.me/e/e3q8)