fix provision_config when destination is a symlink

fix provision_config when dst is a symlink:

Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/aminator/util/linux.py", line 366, in install_provision_config
    shutil.copy(dst,backup)
  File "/usr/lib/python2.7/shutil.py", line 117, in copy
    copyfile(src, dst)
  File "/usr/lib/python2.7/shutil.py", line 82, in copyfile
    with open(src, 'rb') as fsrc:
IOError: [Errno 2] No such file or directory: ...