make the build script independent of Buildkite

This allows us to run the unit tests reliably on local machines as well.

Signed-off-by: Andreea Florescu <fandree@amazon.com>

Author: andreeaflorescu

.buildkite/hooks/post-checkout

@@ -1,18 +1,21 @@
 #!/bin/bash
 
+set -e
+
 DEB_NAME="kernel-image-4.9.0-13-amd64-di_4.9.228-1_amd64.udeb"
 DEB_URL="http://ftp.us.debian.org/debian/pool/main/l/linux/${DEB_NAME}"
 
-REPO_PATH="${BUILDKITE_BUILD_CHECKOUT_PATH}"
-DEB_PATH="${REPO_PATH}/${DEB_NAME}"
-EXTRACT_PATH="${REPO_PATH}/src/bzimage-archive"
+TMP_PATH="/tmp/linux-loader/"
+DEB_PATH="${TMP_PATH}/${DEB_NAME}"
+EXTRACT_PATH="${TMP_PATH}/src/bzimage-archive"
 BZIMAGE_PATH="${EXTRACT_PATH}/boot/vmlinuz"
+SCRIPTPATH="$( cd "$(dirname "$0")" >/dev/null 2>&1 ; pwd -P )"
 
 mkdir -p ${EXTRACT_PATH}
 
-wget $DEB_URL -P ${REPO_PATH}
+wget $DEB_URL -P ${TMP_PATH}
 dpkg-deb -x ${DEB_PATH} ${EXTRACT_PATH}
 
-mv ${BZIMAGE_PATH} ${REPO_PATH}/src/loader/x86_64/bzimage/bzimage
+mv ${BZIMAGE_PATH} "${SCRIPTPATH}/../src/loader/x86_64/bzimage/bzimage"
 rm -r ${EXTRACT_PATH}
 rm -f ${DEB_PATH}