recovery: Split main() into recovery_main.cpp.

This prepares for moving more codes from recovery into librecovery, so
that they will become more easily testable. recovery_main.cpp will be
the source code for recovery module, with the rest moved into
librecovery. recovery_main.cpp mainly does the initializations, such as
setting up the logger.

Test: mmma -j bootable/recovery
Test: recovery_component_test
Test: Build and boot into recovery image on marlin.
Change-Id: I8e846524546b6f3f0e32ed869e851f62261eef23
(cherry picked from commit c241cb662440551eb0d2f42345f7ee08cf60a7dd)
diff --git a/Android.mk b/Android.mk
index 5b71bd3..57b1803 100644
--- a/Android.mk
+++ b/Android.mk
@@ -126,6 +126,7 @@
     device.cpp \
     fuse_sdcard_provider.cpp \
     recovery.cpp \
+    recovery_main.cpp \
     roots.cpp \
     rotate_logs.cpp \