Do not leek orphaned processes

In some environments java processes are left orpened as it is the wrapping sh proccess who reciews SIGTERM.

```
hudson   29290 26348  0 02:57 ?        00:00:00 sh -c java -jar jenkins-lts-rc.war --ajp13Port=-1 --controlPort=52848 --httpPort=52848 2>&1
hudson   29292 29290  0 02:57 ?        00:01:05 java -jar jenkins-lts-rc.war --ajp13Port=-1 --controlPort=52848 --httpPort=52848
```
becomes
```
hudson   29292     1  0 02:57 ?        00:01:05 java -jar jenkins-lts-rc.war --ajp13Port=-1 --controlPort=52848 --httpPort=52848
```
Fix post build step plugin button ambiguity