Switch from sh to bash to match Servo style guide

Originally, I restricted these scripts to pure sh to avoid too many
compatibility issues between Linux and OS X, but I've changed my mind
and now prefer using bash to gain a few nice features.

.travis/dispatch.sh

@@ -1,7 +1,8 @@
-#!/usr/bin/env sh
+#!/usr/bin/env bash
 
 set -o errexit
 set -o nounset
+set -o pipefail
 
 travis_fold_start () {
     printf "travis_fold:start:$1\n"
@@ -31,14 +32,14 @@ run_salt () {
 }
 
 
-if [ "${SALT_NODE_ID}" = "test" ]; then
+if [[ "${SALT_NODE_ID}" == "test" ]]; then
     # Using .travis.yml to specify Python 3.5 to be preinstalled, just to check
     printf "Using $(python3 --version) at $(which python3)\n"
 
     # Run test suite separately for parallelism
     ./test.py
 else
-    if [ "${SALT_FROM_SCRATCH}" = "true" ]; then
+    if [[ "${SALT_FROM_SCRATCH}" == "true" ]]; then
         run_salt 'scratch'
     else
         git fetch origin master:master
@@ -51,7 +52,7 @@ else
 
     # Only run tests against the new configuration
     # TODO: don't hard-code this
-    if [ "${SALT_NODE_ID}" = "servo-master1" ]; then
+    if [[ "${SALT_NODE_ID}" == "servo-master1" ]]; then
         ./test.py sls.buildbot.master sls.nginx
     fi
 fi

.travis/install_salt.sh

@@ -1,11 +1,12 @@
-#!/usr/bin/env sh
+#!/usr/bin/env bash
 
 set -o errexit
 set -o nounset
+set -o pipefail
 
 install_salt () {
     # Ensure that pinned versions match as closely as possible
-    if [ "${OS_NAME}" = "linux" ]; then
+    if [[ "${OS_NAME}" == "linux" ]]; then
         printf "$0: installing salt for Linux\n"
         # Use Trusty (Ubuntu 14.04) on Travis
         # Don't autostart services
@@ -14,7 +15,7 @@ install_salt () {
         printf 'deb http://repo.saltstack.com/apt/ubuntu/14.04/amd64/archive/2015.5.8 trusty main\n' | sudo tee /etc/apt/sources.list.d/saltstack.list >/dev/null
         sudo apt-get -y update
         sudo apt-get -y install salt-minion=2015.5.8+ds-1
-    elif [ "${OS_NAME}" = "osx" ]; then
+    elif [[ "${OS_NAME}" == "osx" ]]; then
         printf "$0: installing salt for Mac OS X\n"
         brew update
         brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/3461c9c74b2f3aba9a6fbd7165823c81dc2b4792/Formula/saltstack.rb
@@ -63,16 +64,16 @@ while true; do
     esac
 done
 
-if [ "$#" -lt 1 ]; then
+if [[ "$#" -lt 1 ]]; then
     printf >&2 "usage: $0 [-c <config_dir> [-F]] [--] os_name\n"
     exit 1
 fi
 
 OS_NAME="$1"
-if [ -z "${CONFIGURE_ONLY}" ]; then
+if [[ -z "${CONFIGURE_ONLY}" ]]; then
     install_salt
 fi
 
-if [ -n "${TEMPORARY_CONFIG_DIR}" ]; then
+if [[ -n "${TEMPORARY_CONFIG_DIR}" ]]; then
     configure_salt
 fi

.travis/setup_salt_roots.sh

@@ -1,7 +1,8 @@
-#!/usr/bin/env sh
+#!/usr/bin/env bash
 
 set -o errexit
 set -o nounset
+set -o pipefail
 
 setup_salt_roots () {
     sudo rm -rf /srv/salt

tests/lint/shebang.py

@@ -11,7 +11,7 @@
 
 INTERPRETERS = {
     'py': 'python3',
-    'sh': 'sh'
+    'sh': 'bash'
 }