t/open.t: Workarounds for Android and Blackberry 10

Howdy!

Quick disclaimer: Android support just got into the perl core. Blackberry 10/embedded QNX NTO isn't merged yet.

That aside, the issue with both of those platforms is that 'true' and several other commands, like echo and pwd, are a shell builtins without an external binary, so three-arg open won't work; you need to either use two-arg open, which implicitly creates a subshell, or still use three-arg but instead pass something like 'sh', '-c', 'true $@', '--'

This pull request does the latter, but only for these OSs.