Allow to have a=b=c, where a is key and b=c is value.

slapos/recipe/build.py

@@ -259,7 +259,7 @@ class Script:
         raise zc.buildout.UserError('Line %r in environment is incorrect' %
           line)
 
-      key, value = line.split('=')
+      key, value = line.split('=', 1)
       key = key.strip()
       value = value.strip()
       if key in wanted_env: