build/base: ensure Red Hat family OS use en_US.UTF-8 locale

ensure en_US.UTF-8 is the default locale on Red Hat systems, since we
are already going this on Debian systems.
If not doing this, that could lead to locale issues during deployments.
Merge pull request #165 from enovance/default-locale-rh

build/base: ensure Red Hat family OS use en_US.UTF-8 locale