Setup sample host name in default_vars

If configured host name is empty, Drupalizer will construct an invalid `sed`
invocation to modify `/etc/hosts` file. As the result, environment
initialization will fail.

default_vars.py

@@ -23,7 +23,7 @@ env.site_db_user = 'dev'
 env.site_db_pass = 'dev'
 env.site_db_host = 'localhost'
 env.site_db_name = 'dev'
-env.site_hostname = ''
+env.site_hostname = 'drupalizer.dev.local'
 env.site_admin_user = 'admin'
 env.site_admin_pass = 'admin'
 env.site_subdir = 'default'