Async interface for running odrefresh

This creates a variant of startTestOdrefresh that uses the
ICompilationTask async mechanism of startTestCompile.

OdrefreshTask implements ICompilationTask; instead of owning a spawned
odrefresh process it owns the VM and runs the blocking call to compsvc
inside a thread.

Add a new command to composd_cmd to exercise this.

Test: composd_cmd async-odrefresh
Bug: 209572296
Change-Id: I3780d40876dbca17d4e2a3d8f7c2b809f5561aee
diff --git a/compos/composd/src/composd_main.rs b/compos/composd/src/composd_main.rs
index 67b5974..2915a58 100644
--- a/compos/composd/src/composd_main.rs
+++ b/compos/composd/src/composd_main.rs
@@ -24,6 +24,7 @@
 mod instance_starter;
 mod internal_service;
 mod odrefresh;
+mod odrefresh_task;
 mod service;
 mod util;