Fix '_create_instance' in config_unittest
Fix '_create_instance' in config_unittest

Previously '_create_instance' would initialize the config object every
time it would be called. This causes '_WriteConfig' to fail with
ConfigurationError: The configuration file has been modified since the
last write. Fix this by passing the config object to '_create_instance'
method.

Signed-off-by: Ilias Tsitsimpis <7f657306c3c5f1ef1cfa2e11204de3febce40ef6@grnet.gr>
Reviewed-by: Jose A. Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>

yiannist/ganeti,bitemyapp/ganeti,ganeti/ganeti,grnet/snf-ganeti,andir/ganeti,andir/ganeti,ganeti/ganeti,onponomarev/ganeti,bitemyapp/ganeti,dimara/ganeti,onponomarev/ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,ganeti/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,mbakke/ganeti,leshchevds/ganeti,grnet/snf-ganeti,mbakke/ganeti,yiannist/ganeti,mbakke/ganeti,apyrgio/ganeti,andir/ganeti,yiannist/ganeti,apyrgio/ganeti,dimara/ganeti