travis-ci: move Travis CI code into dedicated scripts

Most of the Travis CI commands are in the '.travis.yml'. The yml format
does not support functions and therefore code duplication is necessary
to run commands across all builds.

To fix this, add a library for common CI functions. Move all Travis CI
code into dedicated scripts and make them call the library first.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

ci/run-linux32-docker.sh

@@ -0,0 +1,23 @@
+#!/bin/sh
+#
+# Download and run Docker image to build and test 32-bit Git
+#
+
+. ${0%/*}/lib-travisci.sh
+
+docker pull daald/ubuntu32:xenial
+
+# Use the following command to debug the docker build locally:
+# $ docker run -itv "${PWD}:/usr/src/git" --entrypoint /bin/bash daald/ubuntu32:xenial
+# root@container:/# /usr/src/git/ci/run-linux32-build.sh
+
+docker run \
+	--interactive \
+	--env DEVELOPER \
+	--env DEFAULT_TEST_TARGET \
+	--env GIT_PROVE_OPTS \
+	--env GIT_TEST_OPTS \
+	--env GIT_TEST_CLONE_2GB \
+	--volume "${PWD}:/usr/src/git" \
+	daald/ubuntu32:xenial \
+	/usr/src/git/ci/run-linux32-build.sh $(id -u $USER)