so-yaml.py: tolerate missing ancestors in removeKey

replace calls removeKey before addKey, so running `so-yaml.py replace`
on a new dotted key whose parent doesn't exist — e.g., postgres.auth
fanning postgres.telegraf.user into a minion pillar file that has
never carried any postgres.* keys — crashed with
    KeyError: 'postgres'
from removeKey recursing into a missing parent dict.

Make removeKey a no-op when an intermediate key is absent so that:
  - `remove` has the natural "remove if exists" semantics, and
  - `replace` works for brand-new nested keys.

salt/manager/tools/sbin/so-yaml.py

@@ -285,7 +285,8 @@ def add(args):
 def removeKey(content, key):
     pieces = key.split(".", 1)
     if len(pieces) > 1:
-        removeKey(content[pieces[0]], pieces[1])
+        if pieces[0] in content:
+            removeKey(content[pieces[0]], pieces[1])
     else:
         content.pop(key, None)