global rename of MOUNTTABLE_ROOT to NAMESPACE_ROOT. This affects scripts and Makefiles in JS land as well as go.
global rename of MOUNTTABLE_ROOT to NAMESPACE_ROOT. This affects
scripts and Makefiles in JS land as well as go.

veyron/runtimes/google/rt: allow multiple roots to be specified.

Change-Id: I2bdfa600dddf69f8911af0c0c33139ba8cb0c42e

vanadium/js,vanadium/js,vanadium/js,vanadium/js