loader: Rework of load_dynamic_module.

* Split off load_dlopen to perform actual dlopen, check results and log
  warnings when needed.
* Always use RTLD_NOW.
* Use flags which minimize number of calls to dlopen required.  First
  attempt always uses RTLD_GLOBAL when global_symbols_only is enabled,
  RTLD_LOCAL when it is not.

This patch significantly reduces the number of dlopen's performed.  With
299 modules my system ran dlopen 857 times before this patch, 655 times
after this patch.

Change-Id: Ib2c9903cfddcc01aed3e01c1e7fe4a3fb9af0f8b