Fix installation when ant-media-server directory already exists

Example output during installation:

```
Archive:  ams_enterprise.zip
  inflating: /tmp/ant-media-server/ant-media-server.jar  
Archive:  ams_enterprise.zip
replace ant-media-server/ant-media-server.jar? [y]es, [n]o, [A]ll, [N]one, [r]ename: 
```