changed: build opm-common python extension using cmake

only use setup.py to generate wheels. adjust pypi packaging
accordingly

python/install.py

@@ -7,9 +7,10 @@ import filecmp
 src_root = sys.argv[1]
 target_prefix = sys.argv[2]
 install = int(sys.argv[3])
-target_destdir = os.environ.get("DESTDIR", "")
-if target_destdir != "":
-    target_prefix = target_destdir + target_prefix
+if install:
+    target_destdir = os.environ.get("DESTDIR", "")
+    if target_destdir != "":
+        target_prefix = target_destdir + target_prefix
 
 if not os.path.isdir(src_root):
     sys.exit("No such directory: {}".format(src_root))