[FLINK-3517] [dist] Only count active PIDs in start script

[uce]

$ bin/start-cluster.sh
Starting cluster.
Starting jobmanager daemon on host pablo.
Starting taskmanager daemon on host pablo.
$ bin/taskmanager.sh start
[INFO] 1 instance(s) of taskmanager are already running on pablo.
Starting taskmanager daemon on host pablo.
$ bin/taskmanager.sh start
[INFO] 2 instance(s) of taskmanager are already running on pablo.
Starting taskmanager daemon on host pablo.
$ bin/taskmanager.sh start
[INFO] 3 instance(s) of taskmanager are already running on pablo.
Starting taskmanager daemon on host pablo.
$ jps
27328 TaskManager
27140 TaskManager
26949 TaskManager
26523 JobManager
26716 TaskManager
$ kill -9 27140
$ bin/taskmanager.sh start
>>> [INFO] 3 instance(s) of taskmanager are already running on pablo <<< Correct now
Starting taskmanager daemon on host pablo.
$ bin/stop-cluster.sh
Stopping taskmanager daemon (pid: 27545) on host pablo.
Stopping jobmanager daemon (pid: 26523) on host pablo.
$ bin/taskmanager.sh stop
Stopping taskmanager daemon (pid: 27328) on host pablo.
$ bin/taskmanager.sh stop
No taskmanager daemon (pid: 27140) is running anymore on pablo.
$ bin/taskmanager.sh stop
Stopping taskmanager daemon (pid: 26949) on host pablo.
$ bin/taskmanager.sh stop
Stopping taskmanager daemon (pid: 26716) on host pablo.
$ bin/taskmanager.sh stop
No taskmanager daemon to stop on host pablo.

We can further improve the stop part by repeatedly the PIDs in the pid file if a value is not matching an active PID.

[mxm]

+1 to merge!

I find "No taskmanager daemon (pid: 27140) is running anymore on pablo." confusing. I think we could change it to something like "TaskManager couldn't be stopped. It has already been shut down." Anyways, it's not part of this issue.

[tillrohrmann]

Code changes look good :-) +1 for merging.

[uce]

I'm merging this to master and release-1.0.