Extract a library for common CompOS things

A small refactoring as a preliminary step to creating composd.

Create a Rust library for useful things shared by various
CompOS-related binaries. This initially includes the code to start the
VM and connect to CompOS, as well as various useful constants.

As part of extracting the start VM code I migrated to using logging
directly rather than writing to stdout/stderr for greater reusability,
as suggested by Victor.

Bug: 186126194
Test: Get odsign to run compos_verify_key, still works
Change-Id: I57b7ebcdd1a6cb604b5d739b8a8e028fd59e7b90
diff --git a/compos/Android.bp b/compos/Android.bp
index 6705ea8..2af19c8 100644
--- a/compos/Android.bp
+++ b/compos/Android.bp
@@ -12,6 +12,7 @@
         "libbinder_rpc_unstable_bindgen",
         "libbinder_rs",
         "libclap",
+        "libcompos_common",
         "liblibc",
         "liblog_rust",
         "libminijail_rust",
@@ -40,6 +41,7 @@
         "libbinder_rpc_unstable_bindgen",
         "libbinder_rs",
         "libclap",
+        "libcompos_common",
         "liblibc",
         "liblog_rust",
         "libminijail_rust",