ovsdb: ovsdb-dot.in: Change exception semantics for Python3

PEP-3110 changes the semantics for capturing exceptions in Python3
from 'except E,N' to 'except E as N'. This fixes the following problem
when building with python3

SyntaxError: invalid syntax
  File "./ovsdb/ovsdb-dot.in", line 106
    except ovs.db.error.Error, e:
                             ^
SyntaxError: invalid syntax

Link: https://www.python.org/dev/peps/pep-3110/
Signed-off-by: Markos Chandras <[email protected]>
Signed-off-by: Ben Pfaff <[email protected]>

ovsdb/ovsdb-dot.in

@@ -81,7 +81,7 @@ if __name__ == "__main__":
             options, args = getopt.gnu_getopt(sys.argv[1:], 'hV',
                                               ['no-arrows',
                                                'help', 'version',])
-        except getopt.GetoptError, geo:
+        except getopt.GetoptError as geo:
             sys.stderr.write("%s: %s\n" % (argv0, geo.msg))
             sys.exit(1)
 
@@ -103,7 +103,7 @@ if __name__ == "__main__":
 
         schemaToDot(args[0], arrows)
 
-    except ovs.db.error.Error, e:
+    except ovs.db.error.Error as e:
         sys.stderr.write("%s: %s\n" % (argv0, e.msg))
         sys.exit(1)