scripts: cros_sdk: have goma & reclient args check paths

Check these paths exist via the command line parser.

BUG=b:191307774
TEST=`cros_sdk` still works

Change-Id: I11a45964a91ff6a3321069389b4ba39315e510e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4225322
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
diff --git a/scripts/cros_sdk.py b/scripts/cros_sdk.py
index f662912..6a66380 100644
--- a/scripts/cros_sdk.py
+++ b/scripts/cros_sdk.py
@@ -777,17 +777,17 @@
     parser.add_argument(
         "--goma-dir",
         "--goma_dir",
-        type="path",
+        type="dir_exists",
         help="Goma installed directory to mount into the chroot.",
     )
     parser.add_argument(
         "--reclient-dir",
-        type="path",
+        type="dir_exists",
         help="Reclient installed directory to mount into the chroot.",
     )
     parser.add_argument(
         "--reproxy-cfg-file",
-        type="path",
+        type="file_exists",
         help="Config file for re-client's reproxy used for remoteexec.",
     )
     parser.add_argument(