Allow create-cluster to be run from other dirs, not just its own dir

[enjoy-binbin]

The current harcode directory causes us to only run create-cluster
in the create-cluster directory. This PR makes it possible to run
create-cluster from any dir, not just its own dir.

local test:

[root@binblog incubator-kvrocks]# pwd
/root/kvrocks/incubator-kvrocks
[root@binblog incubator-kvrocks]# ./utils/create-cluster/create-cluster start
Starting 30001
instance port 30001 is not ready, will retry after 1 second
OK
OK
Starting 30002
instance port 30002 is not ready, will retry after 1 second
OK
OK
Starting 30003
instance port 30003 is not ready, will retry after 1 second
OK
OK
Starting 30004
instance port 30004 is not ready, will retry after 1 second
OK
OK
Starting 30005
instance port 30005 is not ready, will retry after 1 second
OK
OK
Starting 30006
instance port 30006 is not ready, will retry after 1 second
OK
OK

[git-hulk]

LGTM, great!