Faster `find` for bazel-out in mixed_*

Don't have `find` list *everything* under `out/` and then grep.
Instead, leverage `find`'s options.

Test: TBD?
Change-Id: Idf4b2ecfdcd978edb45b00216b7886909188884e
diff --git a/ci/mixed_droid.sh b/ci/mixed_droid.sh
index f3c0837..e756f8f 100755
--- a/ci/mixed_droid.sh
+++ b/ci/mixed_droid.sh
@@ -13,7 +13,7 @@
 
 # Verify there are artifacts under the out directory that originated from bazel.
 echo "Verifying OUT_DIR contains bazel-out..."
-if find out/ | grep bazel-out &>/dev/null; then
+if find out/ -type d -name bazel-out &>/dev/null; then
   echo "bazel-out found."
 else
   echo "bazel-out not found. This may indicate that mixed builds are silently not running."
diff --git a/ci/mixed_libc.sh b/ci/mixed_libc.sh
index 089a6e7..f013dda 100755
--- a/ci/mixed_libc.sh
+++ b/ci/mixed_libc.sh
@@ -23,7 +23,7 @@
 
 # Verify there are artifacts under the out directory that originated from bazel.
 echo "Verifying OUT_DIR contains bazel-out..."
-if find out/ | grep bazel-out &>/dev/null; then
+if find out/ -type d -name bazel-out &>/dev/null; then
   echo "bazel-out found."
 else
   echo "bazel-out not found. This may indicate that mixed builds are silently not running."