beta: properly connect to parsoid instance

The wmf-beta-autoupdate.py script runs as the mwdeploy user. Thus the
ssh commands to the parsoid instance would fail because that user does
not have any ssh credential to connect there (jenkins-deploy has).

This patch introduce a new tiny shell wrapper to let us execute the
parsoid init script on deployment-parsoid2. It must be run as the
mwdeploy user (like wmf-beta-autoupdate.py) and will sudo as
jenkins-deploy to have the proper credentials.

A new sudo policy is added to let mwdeploy execute the shell wrapper as
jenkins-deploy.

bug: 57233
Change-Id: I0fa1beba0f7e91b0999d6820b20a7569eb735087