Encryption patch follow-up

* PBKDF2 implementation changed to OpenSSL implementation.

* HKDF implementation moved to its own file and tests
  added to ensure correctness.

* Removed libzfs's now unnecessary dependency on libzpool
  and libicp.

* Ztest can now create and test encrypted datasets. This is
  currently disabled until issue #6526 is resolved, but
  otherwise functions as advertised.

* Several small bug fixes discovered after enabling ztest
  to run on encrypted datasets.

* Fixed coverity defects added by the encryption patch.

* Updated man pages for encrypted send / receive behavior.

* Fixed a bug where encrypted datasets could receive
  DRR_WRITE_EMBEDDED records.

* Minor code cleanups / consolidation.

Signed-off-by: Tom Caputi <tcaputi@datto.com>

config/user-libssl.m4

@@ -0,0 +1,12 @@
+dnl #
+dnl # Check for libssl. Used for userspace password derivation via PBKDF2.
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_USER_LIBSSL], [
+	LIBSSL=
+
+	AC_CHECK_HEADER([openssl/evp.h], [], [AC_MSG_FAILURE([
+        *** evp.h missing, libssl-devel package required])])
+
+	AC_SUBST([LIBSSL], ["-lssl -lcrypto"])
+	AC_DEFINE([HAVE_LIBSSL], 1, [Define if you have libssl])
+])

config/user.m4

@@ -13,6 +13,7 @@ AC_DEFUN([ZFS_AC_CONFIG_USER], [
 	ZFS_AC_CONFIG_USER_LIBBLKID
 	ZFS_AC_CONFIG_USER_LIBATTR
 	ZFS_AC_CONFIG_USER_LIBUDEV
+	ZFS_AC_CONFIG_USER_LIBSSL
 	ZFS_AC_CONFIG_USER_FRAME_LARGER_THAN
 	ZFS_AC_CONFIG_USER_RUNSTATEDIR
 	ZFS_AC_CONFIG_USER_MAKEDEV_IN_SYSMACROS