Allow salt group to run salt-call as root

Summary:
By default, salt-call runs to the current user. As such, we should
allow to use as root to avoid to first have to touch files/directory,
then to .

Furthermore, it's not convenient to install packages or chown.

Security implication is salt group's members have a root access
to the Salt master too, currently Ysul, in addition to other servers.

Ref. T795.

Test Plan: sudo salt-call --local test.ping

Reviewers: Sandlayth

Reviewed By: Sandlayth

Differential Revision: https://devcentral.nasqueron.org/D977