shadow: upgrade 4.2.1 -> 4.6

shadow: upgrade 4.2.1 -> 4.6

The following patches are removed because problems have been fixed in this version.
  0001-shadow-CVE-2017-12424
  fix-installation-failure-with-subids-disabled.patch
  usermod-fix-compilation-failure-with-subids-disabled.patch
  CVE-2017-2616.patch
  check_size_of_uid_t_and_gid_t_using_AC_CHECK_SIZEOF.patch
  0001-Do-not-read-login.defs-before-doing-chroot.patch

The following patches are rebased.
  0001-Disable-use-of-syslog-for-sysroot.patch
  0001-useradd-copy-extended-attributes-of-home.patch
  0001-useradd.c-create-parent-directories-when-necessary.patch
  allow-for-setting-password-in-clear-text.patch

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>