compsvc: run odrefresh in the VM

On request, compsvc is responsible to prepare an authfs mountpoint and
specify expected environment variables and command line flags to
odrefresh.

Bug: 205750213
Test: atest ComposHostTestCases # no regression
Change-Id: Ib3c5e5f85e7c76616f1a0937bd43466078598701
diff --git a/authfs/service/src/authfs.rs b/authfs/service/src/authfs.rs
index 2d4f707..e1d820a 100644
--- a/authfs/service/src/authfs.rs
+++ b/authfs/service/src/authfs.rs
@@ -67,6 +67,14 @@
         })?;
         Ok(ParcelFileDescriptor::new(file))
     }
+
+    fn getMountPoint(&self) -> binder::Result<String> {
+        if let Some(s) = self.mountpoint.to_str() {
+            Ok(s.to_string())
+        } else {
+            Err(new_binder_exception(ExceptionCode::SERVICE_SPECIFIC, "Bad string encoding"))
+        }
+    }
 }
 
 impl AuthFs {