Deal with cert generation taking too long, re...

...place with extra retries and add cmdline flag in case someone has a much slower system

replaces #270, which didn't do enough for the VM I have.

- this increases the number of retries (ie, has no effect on faster booting systems),
- adds a `--retries=45` and `--waittime=300` flags to allow it to be set in someone's `config` file
- changes one of the `.` 's into `o`, so you can tell the difference between wait for sshd and then wait for docker daemon

@gmlewis @bfirsh, @tianon please consider :)