Adapt imports to moved path in slapos.recipe.build

In slapos.recipe.build >= 0.57, code slapos/recipe/__init__.py
(which is a legacy namespace) was moved to slapos/recipe/utils.py

Also version up slapos.recipe.build requirement to >= 0.57

setup.py

@@ -43,7 +43,7 @@ setup(
     install_requires=[
         'zc.buildout>=2',
         'setuptools',
-        'slapos.recipe.build>=0.49',
+        'slapos.recipe.build>=0.57',
     ],
     extras_require={
         'test': ['zope.testing', 'manuel'],

slapos/recipe/cmmi/__init__.py

@@ -10,10 +10,12 @@ import sys
 import zc.buildout
 from zc.buildout import UserError
 from zc.buildout.buildout import bool_option
-from .. import (
+from ..utils import (
   # from slapos.recipe.build
-  EnvironMixin, Shared, downloadunpacked, is_true, rmtree
+  EnvironMixin, Shared, is_true, rmtree
 )
+# from slapos.recipe.build
+from .. import downloadunpacked
 
 startup_environ = os.environ.copy()