Get the real extension if log file is gzipped

Udev collector compresses crash log and appends .gz as file extension
which is not recognized by crash sender. This patch fixes crash sender
by extracting real file extension if the original log file ends with
.gz.

BUG=chromium-os:35968
TEST=Manually test, crash sender can send udev collector generated
     log file: report id 7fa1184e8e62946f.

Change-Id: Ic0abd9f264ef601399cc5edd27faa6f64cd9f204
Reviewed-on: https://gerrit.chromium.org/gerrit/37136
Reviewed-by: Michael Krebs <mkrebs@chromium.org>
Reviewed-by: Simon Que <sque@chromium.org>
Commit-Ready: Yufeng Shen <miletus@chromium.org>
Tested-by: Yufeng Shen <miletus@chromium.org>

crash_reporter/crash_sender

@@ -202,7 +202,14 @@ get_base() {
 }
 
 get_extension() {
-  echo "${1##*.}"
+  local extension="${1##*.}"
+  local filename="${1%.*}"
+  # For gzipped file, we ignore .gz and get the real extension
+  if [ "${extension}" = "gz" ]; then
+    echo "${filename##*.}"
+  else
+    echo "${extension}"
+  fi
 }
 
 # Return which kind of report the given metadata file relates to