[cdc_stream] Add a CLI client to start/stop asset streaming sessions (#4)

Implements the cdc_stream client and adjusts asset streaming in
various places to work better outside of a GGP environment.

This CL tries to get quoting for SSH commands right. It also brings
back the ability to start a streaming session from
asset_stream_manager.

Also cleans up Bazel targets setup. Since the sln file is now in root,
it is no longer necessary to prepend ../ to relative filenames to
make clicking on errors work.

common/path.h

@@ -130,6 +130,9 @@ std::string GetDrivePrefix(const std::string& path);
 // Gets the current working directory.
 std::string GetCwd();
 
+// Sets the current working directory.
+void SetCwd(const std::string& path);
+
 // Expands a relative path to an absolute path (relative to the current working
 // directory). Also canonicalizes the path, removing any . and .. elements.
 // Note that if the path does not exist or contains invalid characters, it may