Fix #1112: portPropertyFile not written anymore

[rohanKanojia]

Fix #1112

port mappings should be written after we start containers.

Tested on https://github.com/r0haaaan/dmp-demo-project project with and without this patch. With this patch, I was able to see ports.properties file getting generated:

~/work/repos/dmp-demo-project : $ mvn docker:start
[INFO] Scanning for projects...
[INFO] 
[INFO] -----------------------< io.fabric8:dockerfile >------------------------
[INFO] Building dmp-sample-dockerfile 0.30-SNAPSHOT
[INFO] --------------------------------[ war ]---------------------------------
[INFO] 
[INFO] --- docker-maven-plugin:0.30-SNAPSHOT:start (default-cli) @ dockerfile ---
[INFO] DOCKER> [test-db:latest] "dockerfile": Start container 32772f1b0130
[INFO] DOCKER> [test-db:latest] "dockerfile": Pausing for 5000 ms
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  6.936 s
[INFO] Finished at: 2019-07-27T21:53:29+05:30
[INFO] ------------------------------------------------------------------------
~/work/repos/dmp-demo-project : $ cat src/main/resources/ports.properties 
#Docker ports
#Sat Jul 27 21:53:29 IST 2019
host.port=32787
~/work/repos/dmp-demo-project : $ 

[rhuss]

Thanks !