ceph: Modify ceph package so that it compiles and runs fine on nixos

With adding a patch that makes 2 absolute paths into 2 relative paths, ensuring the third-party libraries are available
in the python environment used and wrapping the python tools with wrapPrograms does so that the fixed ceph pkg can
compile and run as intended on NixOS.

pkgs/tools/filesystems/ceph/0002-fix-absolute-include-path.patch

@@ -0,0 +1,19 @@
+diff -ru ceph/src/key_value_store/kv_flat_btree_async.cc ceph-copy/src/key_value_store/kv_flat_btree_async.cc
+--- ceph/src/key_value_store/kv_flat_btree_async.cc	1980-01-02 00:00:00.000000000 +0100
++++ ceph-copy/src/key_value_store/kv_flat_btree_async.cc	2018-02-13 21:49:59.232860487 +0100
+@@ -15,13 +15,13 @@
+ #include "key_value_store/kv_flat_btree_async.h"
+ #include "key_value_store/kvs_arg_types.h"
+ #include "include/rados/librados.hpp"
+-#include "/usr/include/asm-generic/errno.h"
+-#include "/usr/include/asm-generic/errno-base.h"
+ #include "common/ceph_context.h"
+ #include "common/Clock.h"
+ #include "include/types.h"
+ 
+ 
++#include <asm-generic/errno.h>
++#include <asm-generic/errno-base.h>
+ #include <string>
+ #include <iostream>
+ #include <cassert>

pkgs/tools/filesystems/ceph/generic.nix

@@ -86,12 +86,17 @@ let
   };
 
   ceph-python-env = python2Packages.python.withPackages (ps: [ 
-	ps.sphinx
-	ps.flask
-	ps.argparse
-	ps.cython 
-	ps.setuptools
-	ps.pip
+    ps.sphinx
+    ps.flask
+    ps.argparse
+    ps.cython 
+    ps.setuptools
+    ps.pip
+    # Libraries needed by the python tools
+    ps.Mako
+    ps.pecan
+    ps.prettytable
+    ps.webob
 	]);
 
 in
@@ -103,11 +108,13 @@ stdenv.mkDerivation {
   patches = [ 
  #	 ./ceph-patch-cmake-path.patch
     ./0001-kv-RocksDBStore-API-break-additional.patch   
+  ] ++ optionals stdenv.isLinux [
+    ./0002-fix-absolute-include-path.patch
   ];
 
   nativeBuildInputs = [
     cmake
-    pkgconfig which git
+    pkgconfig which git python2Packages.wrapPython
     (ensureNewerSourcesHook { year = "1980"; })
   ];
   
@@ -122,6 +129,7 @@ stdenv.mkDerivation {
   ] ++ optionals hasKinetic [
     optKinetic-cpp-client
   ];
+
   
   preConfigure =''
     # rip off submodule that interfer with system libs
@@ -149,6 +157,10 @@ stdenv.mkDerivation {
     "-DWITH_LIBCEPHFS=OFF"
   ];
 
+  postFixup = ''
+    wrapPythonPrograms
+  '';
+
   enableParallelBuilding = true;
   
   outputs = [ "dev" "lib" "out" "doc" ];