leap_cli should always write to a logfile with maximum verbosity

we need to debug user's problems, and get the maximum verbosity output of deploy runs. however, we don't want the user to get bothered by a leap -v 5 deploy.

so we need this:

• the user should choose whatever verbosity for screen output
• leap_cli should log with maximum verbosity to a file that the user can upload later

we need to decide how to purge the password from the log, and secure it so only the user can see it.

removing passwords can be done by the bugreport script (#3744)

i'm setting this to high prio, cause we currently support users getting leap deployed

(from redmine: created on 2013-09-05, closed on 2015-02-10, relates #3744, relates #4428 (closed))