Update bash_completion to not use a temp file

TEST=Tested within chroot and using "repo start ooga b<tab>"

Change-Id: I372d13458fb89571db4cdd7561e91c68e1563941

Review URL: http://codereview.chromium.org/3191012
diff --git a/bash_completion b/bash_completion
index 6a3077c..bc9988a 100644
--- a/bash_completion
+++ b/bash_completion
@@ -200,10 +200,9 @@
 
 _list_repo_projects() {
   local repo=${COMP_WORDS[0]}
-  local manifest=$(mktemp)
-  "$repo" manifest -o "$manifest" >& /dev/null
-  grep 'project name=' "$manifest" | sed 's/.\+name="\([^"]\+\)".\+/\1/'
-  rm -f "$manifest" >& /dev/null
+  "$repo" manifest -o /dev/stdout 2> /dev/null \
+    | grep 'project name=' \
+    | sed 's/.\+name="\([^"]\+\)".\+/\1/'
 }
 
 # Complete repo's <command> argument.