Migrate from google-glog to log4cxx

Finally removes google-glog dependency! (fix #746)

Note that this pull-req depends on #807 and cannot be merged before #807.

* Modifies the following command line options:
  * Adds `--log-config` option.
    Users can now specify XML log4cxx configuration file, which can be used for server/proxy/jubavisor.
  * Removes `--loglevel` option.
    Users should specify desired log levels in XML configuration file.
  * Modifies `--logdir` option.
    This option is now only used for printing ZooKeeper logs.
  * Deprecates `--debug` option for interactive commands (`jubaconfig` and `jubactl`)
    `--debug` option used to have a effect of printing logs to standard output instead of files.
    As I think those commands should not write logs, these commands now always prints their logs to standard output.

* I added `#include <errno.h>` for some files.
  This is because `errno` is being used without including `errno.h`.
  As `glog/logging.h` indirectly includes `errno.h`, the problem did not become apparent until now.

Things left:
* Add sample XML configuration file.
* Remove google-glog from core layer (assertion).
* Update documentation: build instructions and command line option changes.