CI: Move CI code into a single script

.travis.yml

@@ -5,10 +5,4 @@ cache:
   directories:
   - "/opt/shellcheck"
 script:
-- mkdir -p /opt/shellcheck
+- ci/run_shellcheck
-- "[[ ! -e /opt/shellcheck/shellcheck ]] && wget -qO- https://github.com/koalaman/shellcheck/releases/download/stable/shellcheck-stable.linux.x86_64.tar.xz
-  | tar -xJv -O shellcheck-stable/shellcheck | sudo tee /opt/shellcheck/shellcheck
-  > /dev/null || true"
-- sudo chmod +x /opt/shellcheck/shellcheck
-- "/opt/shellcheck/shellcheck --version"
-- "/opt/shellcheck/shellcheck $(grep -lzP '^#!/bin/\\w+sh' -r .)"

ci/run_shellcheck.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+set -o pipefail
+set -o errexit
+set -o nounset
+set -o errtrace
+shopt -s inherit_errexit
+
+ci/run_shellcheck mkdir -p /opt/shellcheck
+[[ ! -e /opt/shellcheck/shellcheck ]] && wget -qO- https://github.com/koalaman/shellcheck/releases/download/stable/shellcheck-stable.linux.x86_64.tar.xz
+  | tar -xJv -O shellcheck-stable/shellcheck | sudo tee /opt/shellcheck/shellcheck
+  > /dev/null || true
+sudo chmod +x /opt/shellcheck/shellcheck
+/opt/shellcheck/shellcheck --version
+/opt/shellcheck/shellcheck $(grep -lzP '^#!/bin/\\w+sh' -r .)