Add new script to fetch tarballs for source installation

This script will be sourced from the build scripts to provide alternate
ways to fetch/generate a source tarball. This tarball can then be
provided to a Dockerfile for source installation.

Change-Id: I0212a83d098b8d83446f69b92c2b07ef39a93c10
Partially-Implements: blueprint install-from-source

tools/gen-source-tar.sh

@@ -0,0 +1,47 @@
+#!/bin/bash
+
+set -e
+
+: ${SOURCE_INSTALL_METHOD:=git}
+: ${GIT_REF:=master}
+: ${LOCAL_SOURCE:=/tmp/${COMPONENT}}
+
+function fetch_source_from_uri {
+    curl ${TARBALL_URI} -o ${TMPDIR}/${COMPONENT}.tar
+}
+
+function fetch_source_from_git {
+    # NOTE(pbourke): do a shallow clone to master only, unless a specific ref is
+    # required
+    if [ -z ${GIT_REF} ]; then
+        git clone --depth=1 ${CLONE_FROM} ${TMPDIR}/${COMPONENT}
+    else
+        git clone ${CLONE_FROM} ${TMPDIR}/${COMPONENT}
+        git --git-dir ${TMPDIR}/${COMPONENT}/.git checkout ${GIT_REF}
+    fi
+    tar -cf ${TMPDIR}/${COMPONENT}.tar -C ${TMPDIR} ${COMPONENT}
+}
+
+function fetch_source_from_local {
+    tar -cf ${TMPDIR}/${COMPONENT}.tar \
+        -C $(dirname ${LOCAL_SOURCE}) ${COMPONENT}
+}
+
+case ${SOURCE_INSTALL_METHOD} in
+    curl)
+        fetch_source_from_uri
+        ;;
+    git)
+        fetch_source_from_git
+        ;;
+    local)
+        fetch_source_from_local
+        ;;
+    *)
+        cat << EOF
+Unknown install method '${SOURCE_INSTALL_METHOD}'. Please check the value of
+\$SOURCE_INSTALL_METHOD in .buildconf
+EOF
+        exit 1
+        ;;
+esac