LUReplaceDisks: remove use of ChainOpCode
LUReplaceDisks: remove use of ChainOpCode

The calls to OpActivateInstanceDisks and OpDeactivateInstanceDisks has
been replaced by _StartInstanceDisks and _SafeShutdownInstanceDisks
respectively. This is the last usage of ChainOpCode.

Reviewed-by: iustinp


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