Skip already installed package.

osdk/cmds.py

@@ -1,4 +1,5 @@
 from typing import Callable, cast
+import os
 
 from osdk.args import Args
 from osdk.context import contextFor
@@ -174,6 +175,10 @@ def installCmd(args: Args):
 
         extPath = f"{const.EXTERN_DIR}/{extSpec}"
 
+        if os.path.exists(extPath):
+            print(f"Skipping {extSpec}, already installed")
+            continue
+
         print(f"Installing {extSpec}-{ext.tag} from {ext.git}...")
         shell.popen("git", "clone", "--depth", "1", "--branch",
                     ext.tag, ext.git, extPath)