Adding more detail on flashing the Rock Pis

Also, small change to change_hostname.sh that calls pi6 the imu on a new
install (where the pi's aren't already written into the file)

And added a modification file to the image for tracking purposes

Change-Id: Ifbc73115f5b0f41b43f557de65843a347cda4678
Signed-off-by: Jim Ostrowski <yimmy13@gmail.com>
diff --git a/frc971/rockpi/build_rootfs.sh b/frc971/rockpi/build_rootfs.sh
index bb8b84a..1eeebf8 100755
--- a/frc971/rockpi/build_rootfs.sh
+++ b/frc971/rockpi/build_rootfs.sh
@@ -12,14 +12,14 @@
 # Check if dependencies are missing.
 missing_deps=()
 REQUIRED_DEPS=(
-    flex
     bison
-    gcc-arm-none-eabi
-    gcc-aarch64-linux-gnu
-    u-boot-tools
-    device-tree-compiler
-    swig
     debootstrap
+    device-tree-compiler
+    flex
+    gcc-aarch64-linux-gnu
+    gcc-arm-none-eabi
+    swig
+    u-boot-tools
 )
 for dep in "${REQUIRED_DEPS[@]}"; do
     if ! dpkg-query -W -f='${Status}' "${dep}" | grep -q "install ok installed"; then
@@ -258,6 +258,13 @@
 
 target "apt-get clean"
 
+# Add a file to show when this image was last modified and by whom
+TIMESTAMP_FILE="${PARTITION}/home/pi/.ImageModifiedDate.txt"
+echo "Date modified:"`date` > "${TIMESTAMP_FILE}"
+echo "Image file: ${IMAGE}"  >> "${TIMESTAMP_FILE}"
+echo "Git tag: "`git rev-parse HEAD` >> "${TIMESTAMP_FILE}"
+echo "User: "`whoami` >> "${TIMESTAMP_FILE}"
+
 sudo chroot ${PARTITION} qemu-aarch64-static /bin/bash
 
 # TODO(austin): This appears to not be working...  pi_target doesn't apper to be happy