Remove directory rabbit-hole from generate_logs output

This patch changes the output tarball from generate_logs to directly
include the diagnostic_logs payload directory, instead of the absolute
path chain through /home/chronos/user/Downloads, which will make the
file easier to handle.

It also changes the compression algorithm to gzip, which reduces the
script's runtime on my log-burdened Link by roughly a factor of 4,
while less than doubling the output size (as the time to copy it over
100baseT is negligible compared to the runtime, I would consider this
an improvement).

BUG=None
TEST=None

Change-Id: Ic2b9a8c5cbc714127599f059a1f07e0421a49a74
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/45287
Reviewed-by: Kris Rambish <krisr@chromium.org>
diff --git a/generate_logs b/generate_logs
index 3560d3a..f13cc7c 100755
--- a/generate_logs
+++ b/generate_logs
@@ -229,7 +229,8 @@
 
 # Compressing the log folder with all collected files.
 currentdate=$(date +%m%d%y-%H%M%S)
-sudo tar cjfP ${tar_path}/log-${currentdate}.tar.bz2 ${log_dir}/
+sudo tar czf ${tar_path}/log-${currentdate}.tar.gz -C $(dirname ${log_dir}) \
+    $(basename ${log_dir})/
 sudo rm -rf ${log_dir}/
 echo "Log files zipped to folder under ${tar_path}: log-${currentdate}.tar.bz2"