compute rpcapi 2.29 is not backwards compatible

patch 6fcf4133b49cfefa77151937dec4db097a85c349 which added compute
rpcapi version 2.29 does not provide any backwards compatibility.

Fix this issue with 'self.can_send_version'

Fix bug 1217068

Change-Id: Idc49040b712058aab8d3ed769bdf18bdc0a4f067
Merge "compute rpcapi 2.29 is not backwards compatible"