Move muranodashboard logs to a separate file.

Default file location is /var/log/murano-dashboard.log
(hard-coded into horizon config, still have to make it
more flexible). In this separate file we have the same
log levels which were specified in code (contrary to
ubiquitous [error] in apache logs).

Fixes: bug MRN-745.

Change-Id: Id4977b40cebba7e1fada055443c6c26ab64d9584