Client/Tools/Action: add shell attribute

Add an option to specify whether a command should be executed within
a shell to enable flow control and other shell-specific syntax.
Merge pull request #97 from AlexanderS/action-add-shell-flag

Client/Tools/Action: add shell attribute
Probes: no need to .save() after .get_or_create()
Reporting: Fix traceback when run interactively

Signed-off-by: Sol Jerome <sol.jerome@gmail.com>