core: install core-<kernel>.o at bin/

By installing the core object to bin/, we follow the same convention as
for regular binaries. This, in turn, enables us to ship core in a
regular binary archive. The patch also adjusts the run tool to pick up
the core object from bin/ for the final linking stage.

tool/run/boot_dir/nova

@@ -1,5 +1,5 @@
 proc binary_name_ld_lib_so { } { return "ld-nova.lib.so" }
-proc binary_name_core_o    { } { return "nova/core.o" }
+proc binary_name_core_o    { } { return "core-nova.o" }
 proc binary_name_timer     { } { return "nova_timer_drv" }