Enable odrefresh to work with composd.

composd spawns odrefresh in its usual domain. odrefresh then spawns
fd_server in a different domain, and makes binder calls back to
composd to perform individual compilation steps.

fd_server is fairly generic, and part of the virt APEX, but this
instance is specific to composd (e.g. it has access to ART files), so
I named the domain composd_fd_server.

Bug: 186126194
Test: Run composd_cmd, artifacts generated
Change-Id: I5a431dd00b5b396a67021c618fc6edcfb25aa21b
diff --git a/apex/com.android.virt-file_contexts b/apex/com.android.virt-file_contexts
index ad8d55c..cc712ff 100644
--- a/apex/com.android.virt-file_contexts
+++ b/apex/com.android.virt-file_contexts
@@ -1,3 +1,4 @@
 (/.*)?                     u:object_r:system_file:s0
 /bin/crosvm                u:object_r:crosvm_exec:s0
+/bin/fd_server             u:object_r:fd_server_exec:s0
 /bin/virtualizationservice u:object_r:virtualizationservice_exec:s0