[6.0-marshmallow branch] add gosu; refactor things

[robbyoconnor]

This will also fix issues with the ccache env vars not showing up -- at least in my testing.

[robbyoconnor]

aosp@2d3c9b0ff45d:/aosp$ env 
HOSTNAME=2d3c9b0ff45d
TERM=xterm
CCACHE_DIR=/tmp/ccache
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
PWD=/aosp
HOME=/home/aosp
SHLVL=1
GOSU_VERSION=1.10
USE_CCACHE=1
_=/usr/bin/env
aosp@2d3c9b0ff45d:/aosp$     

[robbyoconnor]

Fixed a small issue and rebased

[robbyoconnor]

you jus see the process, not a forked process

[robbyoconnor]

that said, hold off on merging this...wanna see if I can fix a small issue...there's a weird issue where I'm seeing an unmet dependency error related to openjdk and wanna fix that

[robbyoconnor]

@kylemanna -- this is ready for showtime -- I think we should use gosu -- the rationale behind why it exists is good -- as well as the fact that it just gets out of the way vs what sudo su, etc do.

Ultimately -- this up to you -- I'm just contributing back my changes :)