Make gridinit_cmd synchronous

[vdombrovski]

Currently, gridinit_cmd doesn't guarantee the proper outcome of the executed commands. E.g. gridinit_cmd restart will return regardless of whether all services have been restarted or not.

This behavior implies that additional checks need to be made on the user side to wait for the commands to actually finish, and sometimes to perform force kills on hanging processes (not recommended but sometimes necessary).

A better behavior would be similar to systemd's systemctl which will not return before the process is restarted, unless a certain timeout is reached (in which case the hanging process gets killed).