Move host library name back to libevent-host.so

There is an argument that this prevents us from using a system provided
library when we intended to use our own. The build system now supports
'unique_host_soname: true' to automatically do this renaming for host
libraries, while still using 'libevent' as the reference within the
build files.

Change-Id: Iefbb7b8f46dbe951d05d9bda262af7998bbc6929
diff --git a/Android.bp b/Android.bp
index f72b4b9..3b9d52b 100644
--- a/Android.bp
+++ b/Android.bp
@@ -15,6 +15,7 @@
 cc_library_shared {
     name: "libevent",
     host_supported: true,
+    unique_host_soname: true,
 
     arch: {
         arm: {