BuildAPI: Add UnmountPath to SDK controller.

Ran api/compile_build_api_proto. This provides a basic entry point stub
and faux unit tests. Implementation with service methods to follow.

BUG=chromium:1095661
TEST=manual, run_tests

Change-Id: I0b492aecdda63ce46d870499042e4ece138de14c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2324080
Reviewed-by: Alex Klein <saklein@chromium.org>
Commit-Queue: Michael Mortensen <mmortensen@google.com>
Tested-by: Michael Mortensen <mmortensen@google.com>
diff --git a/api/controller/sdk.py b/api/controller/sdk.py
index ccf3ee6..3f345e0 100644
--- a/api/controller/sdk.py
+++ b/api/controller/sdk.py
@@ -113,6 +113,14 @@
 
 
 @faux.all_empty
+@validate.require('path.path')
+@validate.validation_complete
+def UnmountPath(input_proto, _output_proto, _config):
+  """Unmount a path"""
+  sdk.UnmountPath(input_proto.path)
+
+
+@faux.all_empty
 @validate.validation_complete
 def Clean(input_proto, _output_proto, _config):
   """Clean unneeded files from a chroot."""