Update examples to use argparse instead of optparse

optparse was deprecated since 2.7 and removed in python 3

Change-Id: Ic5bccb171f45c4948dad47e8fc6fb5830d6dfcff
Fix up usage of argparse in examples

Since a76db4cfc83d4cf7a52d045e4df82ec8b1e3f562 it is broken.

- Use ArgumentDefaultsHelpFormatter to automatically show default
  values for the options.

- Remove hard-coded 'default' information from help texts.

- Add a metavar for the ssh event timeout option.

- Integer arguments must now be specified as `int` rather than
  `'int'` with quotation marks.

- Fix calls to `parser.parse_args`, which now returns a single
  value rather than a tuple.

Change-Id: If5cf4e2d1f4014a60f7a7634d43df12b788bc7b4