Correct flake8 errors after STYLE builder update

Fix new flake8 errors related to bare excepts and ambiguous
variable names due to a STYLE builder update.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Closes #6776

cmd/arcstat/arcstat.py

@@ -238,7 +238,7 @@ def get_terminal_lines():
         data = fcntl.ioctl(sys.stdout.fileno(), termios.TIOCGWINSZ, '1234')
         sz = struct.unpack('hh', data)
         return sz[0]
-    except:
+    except Exception:
         pass