Scripts: improved "apollo.sh clean".

Added "bash apollo.sh clean --help" for usage

apollo.sh

@@ -124,7 +124,7 @@ function _usage() {
     ${BLUE}doc${NO_COLOR}: generate doxygen document
     ${BLUE}clean${NO_COLOR}: cleanup bazel output and log/coredump files
     ${BLUE}format${NO_COLOR}: format C++/Python/Bazel/Shell files
-    ${BLUE}usage${NO_COLOR}: show this message
+    ${BLUE}usage${NO_COLOR}: show this message and exit
     "
 }
 
@@ -199,7 +199,7 @@ function main() {
             env ${APOLLO_ENV} bash "${APOLLO_ROOT_DIR}/scripts/apollo_lint.sh" cpp
             ;;
         clean)
-            env ${APOLLO_ENV} bash "${APOLLO_ROOT_DIR}/scripts/apollo_clean.sh" "-a"
+            env ${APOLLO_ENV} bash "${APOLLO_ROOT_DIR}/scripts/apollo_clean.sh" "$@"
             ;;
         doc)
             env ${APOLLO_ENV} bash "${APOLLO_ROOT_DIR}/scripts/apollo_docs.sh" "$@"

scripts/apollo_clean.sh

@@ -38,9 +38,9 @@ function _clean_bazel_cache() {
 
   # Remove bazel cache in associated directories
   if [ -d /apollo-simulator ]; then
-    pushd /apollo-simulator > /dev/null
+    pushd /apollo-simulator >/dev/null
     bazel clean ${opt}
-    popd > /dev/null
+    popd >/dev/null
   fi
 }
 
@@ -75,11 +75,15 @@ function _print_usage() {
   echo "${TAB}--log       Remove log files"
   echo "${TAB}-a, --all   Equivalent to \"--bazel --core --log\""
   echo "${TAB}--expunge   Run \"bazel clean --expunge\""
-
-  echo "${TAB}-h, --help  Show this message"
+  echo "${TAB}-h, --help  Show this message and exit"
 }
 
 function parse_arguments() {
+  if [[ $# -eq 0 ]]; then
+    _print_usage
+    exit 1
+  fi
+
   while [ $# -gt 0 ]; do
     local opt="$1"
     shift