Fix build_performance.sh to pass shellcheck

Author: mehrdada

tools/run_tests/performance/build_performance.sh

@@ -16,7 +16,7 @@
 source ~/.rvm/scripts/rvm
 set -ex
 
-cd $(dirname $0)/../../..
+cd "$(dirname "$0")/../../.."
 
 CONFIG=${CONFIG:-opt}
 
@@ -28,11 +28,11 @@ then
   # TODO(jtattermusch): not embedding OpenSSL breaks the C# build because
   # grpc_csharp_ext needs OpenSSL embedded and some intermediate files from
   # this build will be reused.
-  make CONFIG=${CONFIG} EMBED_OPENSSL=true EMBED_ZLIB=true qps_worker qps_json_driver -j8
+  make CONFIG="${CONFIG}" EMBED_OPENSSL=true EMBED_ZLIB=true qps_worker qps_json_driver -j8
 fi
 
 PHP_ALREADY_BUILT=""
-for language in $@
+for language in "$@"
 do
   case "$language" in
   "c++")
@@ -53,10 +53,10 @@ do
     fi
     ;;
   "csharp")
-    python tools/run_tests/run_tests.py -l $language -c $CONFIG --build_only -j 8 --compiler coreclr
+    python tools/run_tests/run_tests.py -l "$language" -c "$CONFIG" --build_only -j 8 --compiler coreclr
     ;;
   *)
-    python tools/run_tests/run_tests.py -l $language -c $CONFIG --build_only -j 8
+    python tools/run_tests/run_tests.py -l "$language" -c "$CONFIG" --build_only -j 8
     ;;
   esac
 done