add Jenkinsfile to test each PR and branch commits

This includes a basic test that attempts to compile the rustfmt crate.
Ensures that the workspace is always removed at the end of the build. It
utilizes available caches to speed up the build process and parallelizes
the build across i386, x86_64, arm32, and arm64 targets.

Signed-off-by: Derek Straka <derek@asterius.io>

scripts/cleanup-env.sh

@@ -0,0 +1,5 @@
+#!/bin/bash -e
+
+sudo umount build
+
+exit 0

scripts/fetch.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/bash -x
 
 # the repos we want to check out, must setup variables below
 # NOTE: poky must remain first
@@ -33,7 +33,11 @@ update_repo() {
 		git fetch origin || die "unable to fetch ${uri}"
 	else
 		echo "Cloning '${path}'"
-		git clone ${uri} ${path} || die "unable to clone ${uri}"
+		if [ -z "${GIT_LOCAL_REF_DIR}" ]; then
+			git clone ${uri} ${path} || die "unable to clone ${uri}"
+		else
+			git clone --reference ${GIT_LOCAL_REF_DIR}/`basename ${path}` ${uri} ${path}
+		fi
 		pushd ${path} > /dev/null
 	fi
 

scripts/setup-env.sh

@@ -0,0 +1,7 @@
+#!/bin/bash -e
+
+mkdir -p build
+
+sudo mount -t tmpfs -o size=64G,mode=755,uid=${UID} tmpfs build
+
+exit 0