envsetup.sh: Add buildhost safety net

Linux distros all have little nuances that we
can trip over e.g. currently nodejs is called
'node' on arch but nodejs on Ubuntu, so we
add code to distinguish between distros and
we can put distro specific code here.

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Merge pull request #2 from kraj/master

envsetup.sh: Add buildhost safety net