Don't exit program in run_file

The cli may exit in run_file if there's an error. This is the expected
behavior when running one or more files from the command line and one
fails. But we want to be able to run files from within the current
session, and that should not terminate the program.

Change the semantics of the run_file function to return the status as a
bool.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>