test/ipc: Add test cases for ipc_msg_* functions

test/ipc: Add test cases for ipc_msg_* functions

This commit adds test cases to ensure that ipc_msg_* functions work as
intended. The following functions are covered by the test cases.
 - ipc_msg_get_version()
 - ipc_msg_get_source()
 - ipc_msg_get_destination()
 - ipc_msg_get_user()
 - ipc_msg_get_timestamp()
 - ipc_msg_get_data()
 - ipc_msg_get_signer_name()
 - ipc_msg_get_signer_email()
 - ipc_msg_get_signer_key()