migrate_to action test is missing OCF_RESKEY_CRM_meta_migrate_target environment variable

When testing migrate_to command, the environment variable OCF_RESKEY_CRM_meta_migrate_target must be passed to let agent know about the target node.

Please see http://www.linux-ha.org/doc/dev-guides/_literal_migrate_to_literal_action.html

Start with the migrate_to action test and the linked migrate_to action documentation to understand the expected target-node environment. Ensure the test passes OCF_RESKEY_CRM_meta_migrate_target to the command, then run the relevant test and confirm the agent receives the target node.

Written by the indexing model from the issue text.