Call odrefresh in VM from composd

composd needs to prepare the directory, run a fd_server, etc. then
request to run odrefresh in the VM.

`FdServerConfig` and `FdServer` are introduced to make starting a
fd_server from composd easier.

Also, add a testing command in composd_cmd.

Bug: 205750213
Test: atest ComposHostTestCases
Test: With some local hacks in ART, with SELinux disabled in the VM,
      odrefresh completed with exit code 80 and output files that
      look normal (at least sizes are).
Change-Id: I52c9d1ad369eea6d423831adb42087a3bcf30d66
diff --git a/compos/composd/Android.bp b/compos/composd/Android.bp
index 2ab12e3..735b9a5 100644
--- a/compos/composd/Android.bp
+++ b/compos/composd/Android.bp
@@ -21,6 +21,7 @@
         "libminijail_rust",
         "libnix",
         "libnum_traits",
+        "liblibc",
         "liblog_rust",
         "librustutils",
         "libshared_child",