def load() robustness

[voodoonofx]

When placing the plugin path on a shared network resource which has a potentially flaky connection (Gasp, I know but there's a variety of reason a shared drive (even our GPFS) can go offline, even for 1 minute or so), shotgun should attempt to load the plugin, and failing an OSError, should gracefully refuse to reload the plugin instead of crash. This will have implications on startup if no plugins are able to be found (easy to detect).

For example, the code block at 560 -> 569 should be wrapped in a try, except (OSError), and an additional check should be made to loudly whine (or then crash/email, etc), if no plugins are loaded.