libbtrfsutil: update python setup.py for distribution

Fixes so 'python3 -m build' works and package can be uploaded to pypi
(https://pypi.org/project/btrfsutil/).

- setup.py is still used for local build (make)
- for pypi it must be done by 'python3 -m build' that is build in a
  temporary directory
- btrfsutilpy.h must be also distributed
- version is set manually (the git VERSION file is not accessible)
- the project page metadata is empty, the README.md should be added

Issue: #310
Signed-off-by: David Sterba <dsterba@suse.com>

libbtrfsutil/python/setup.py

@@ -70,7 +70,12 @@ void add_module_constants(PyObject *m)
 
 class my_build_ext(build_ext):
     def run(self):
-        if out_of_date(['../btrfsutil.h'], 'constants.c'):
+        # Running dist outside of git
+        if not os.path.exists('../btrfsutil.h'):
+            # But no generated constants.c found
+            if not os.path.exists('constants.c'):
+                raise Exception("No generated constants.c found, please fix")
+        elif out_of_date(['../btrfsutil.h'], 'constants.c'):
             try:
                 gen_constants()
             except Exception as e:
@@ -92,6 +97,9 @@ module = Extension(
         'qgroup.c',
         'subvolume.c',
     ],
+    headers=[
+        'btrfsutilpy.h'
+    ],
     include_dirs=['..'],
     library_dirs=['../..'],
     libraries=['btrfsutil'],
@@ -99,7 +107,9 @@ module = Extension(
 
 setup(
     name='btrfsutil',
-    version=get_version(),
+    # FIXME: version file is not present when building outside of git
+    #version=get_version(),
+    version='6.10',
     description='Library for managing Btrfs filesystems',
     url='https://github.com/kdave/btrfs-progs',
     license='LGPLv2+',