utils run_as and run_bg_as should not "su" if user == "root"

[kwmonroe]

Hooks run as root, so if we have places where we call run_[bg_]as(x, user=root), we should drop the ['su', user, '-c'] args to the runner:

https://github.com/juju-solutions/jujubigdata/blob/master/jujubigdata/utils.py#L361

This bit me a couple minutes ago with zookeeper. We were trying to pkill -f the zk rest server with run_as(x, 'root'), which tried to do a 'su root -c "pkill -f x"'.

This is no bueno because the sigterm from pkill will travel back up into the "su root" and cause the runner to return with errno 143. In my case, i simply replaced zk's run_as with a check_call, but it would be nice if we fixed it in the utils methods.