roomservice.py: Use list type for filter() results

A filter() call returns an iterable in python3.
If len(matches) is then checked, you get a nasty error:

[...]
WARNING: Trying to fetch a device that's already there
[...]
  File "vendor/omni/build/tools/roomservice.py", line 56, in check_repo_exists
    if len(matches) != 1:
TypeError: object of type 'filter' has no len()

Change-Id: I48b42e6931bdbc1bfef2203ede0b3dadc8582a56
diff --git a/build/tools/roomservice.py b/build/tools/roomservice.py
index cad299e..8f3641f 100755
--- a/build/tools/roomservice.py
+++ b/build/tools/roomservice.py
@@ -52,7 +52,7 @@
 
 def check_repo_exists(git_data, device):
     re_match = "^android_device_.*_{device}$".format(device=device)
-    matches = filter(lambda x: re.match(re_match, x), git_data)
+    matches = list(filter(lambda x: re.match(re_match, x), git_data))
     if len(matches) != 1:
         raise Exception("{device} not found,"
                         "exiting roomservice".format(device=device))