acu163202 - suppress right_script and powershell providers exec error description
acu163202 Have rightscripts throw an alternate exception type.

This allows us to handle it differently for Exception display handling.
acu163202 Re-enable powershell based provider spec
acu163202 Spec error recipes raise Exec, not RightScriptExec
acu163202 Oops must reraise exception with alternate class for windows

Windows powershell chef class subclasses Execute, unlike rightscript
chef class, which subclasses nothing.  Execute raises a ::Exec exception
via shell_out!, when we want to coerce that into a RightScriptExec
exception.
acu163202 Minor fix
acu163202 Change exception type to Exec since its Chef case
Merge pull request #387 from rightscale/ivory_14_08_acu163202_suppress_error_description_for_right_script_and_powershell_blocks

Ivory 14 08 acu163202 suppress error description for right script and powershell blocks