formatted gcloud completion and used helper function

completion/available/gcloud.completion.bash

@@ -1,9 +1,13 @@
 #/usr/bin/env bash
 # Bash completion for Google Cloud SDK
 
-if which gcloud >/dev/null 2>&1; then
-  GOOGLE_SDK_ROOT=${GOOGLE_SDK_ROOT:-$(gcloud info --format="value(installation.sdk_root)")}
-  for i in $(ls ${GOOGLE_SDK_ROOT}/*.bash.inc); do
-    source $i
-  done
+if _command_exists gcloud
+then
+    # get install path
+    GOOGLE_SDK_ROOT=${GOOGLE_SDK_ROOT:-$(gcloud info --format="value(installation.sdk_root)")}
+
+    # souce all the bash completion file that are available
+    for i in $(ls ${GOOGLE_SDK_ROOT}/*.bash.inc); do
+        source $i
+    done
 fi