[FIX] Odoo 11.0-13.0: set the default shell to bash

It appears that dash can be unpredictable.

Also, uses the `pipefail` as stated in the Dockerfile best practice [1].

[1] https://github.com/docker/docker.github.io/blob/master/develop/develop-images/dockerfile_best-practices.md#using-pipes

13.0/Dockerfile

@@ -1,12 +1,13 @@
 FROM debian:buster-slim
 MAINTAINER Odoo S.A. <info@odoo.com>
 
+SHELL ["/bin/bash", "-xo", "pipefail", "-c"]
+
 # Generate locale C.UTF-8 for postgres and general locale data
 ENV LANG C.UTF-8
 
 # Install some deps, lessc and less-plugin-clean-css, and wkhtmltopdf
-RUN set -x; \
-        apt-get update \
+RUN apt-get update \
         && apt-get install -y --no-install-recommends \
             ca-certificates \
             curl \
@@ -35,8 +36,7 @@ RUN set -x; \
         && rm -rf /var/lib/apt/lists/* wkhtmltox.deb
 
 # install latest postgresql-client
-RUN set -x; \
-        echo 'deb http://apt.postgresql.org/pub/repos/apt/ buster-pgdg main' > /etc/apt/sources.list.d/pgdg.list \
+RUN echo 'deb http://apt.postgresql.org/pub/repos/apt/ buster-pgdg main' > /etc/apt/sources.list.d/pgdg.list \
         && export GNUPGHOME="$(mktemp -d)" \
         && repokey='B97B0AFCAA1A47F044F244A07FCC7D46ACCC4CF8' \
         && gpg --batch --keyserver keyserver.ubuntu.com --recv-keys "${repokey}" \
@@ -48,15 +48,13 @@ RUN set -x; \
         && rm -rf /var/lib/apt/lists/*
 
 # Install rtlcss (on Debian buster)
-RUN set -x; \
-    npm install -g rtlcss
+RUN npm install -g rtlcss
 
 # Install Odoo
 ENV ODOO_VERSION 13.0
 ARG ODOO_RELEASE=20200417
 ARG ODOO_SHA=db29fbcebf63f9f656e9445f462190ac775ee533
-RUN set -x; \
-        curl -o odoo.deb -sSL http://nightly.odoo.com/${ODOO_VERSION}/nightly/deb/odoo_${ODOO_VERSION}.${ODOO_RELEASE}_all.deb \
+RUN curl -o odoo.deb -sSL http://nightly.odoo.com/${ODOO_VERSION}/nightly/deb/odoo_${ODOO_VERSION}.${ODOO_RELEASE}_all.deb \
         && echo "${ODOO_SHA} odoo.deb" | sha1sum -c - \
         && apt-get update \
         && apt-get -y install --no-install-recommends ./odoo.deb \