Stop should respect docker.skip

[doyleyoung]

When command line contains -Ddocker.skip and stop goal configuration contains <executeStopOnVMShutdown>true</executeStopOnVMShutdown> the following code still throws an error:

            if (!invokedTogetherWithDockerStart()) {
                throw new MojoExecutionException("docker:stop with executeStopOnVMShutdown is only possible if" +
                        " the docker containers started within the same maven session.");
            }

This execution should be skipped and there should not be an error.

[codecov]

Codecov Report

Merging #1561 (6842111) into master (3dd6acd) will increase coverage by 0.00%.
The diff coverage is 75.00%.

❗ Current head 6842111 differs from pull request most recent head 77163ed. Consider uploading reports for the commit 77163ed to get more accurate results

@@            Coverage Diff            @@
##             master    #1561   +/-   ##
=========================================
  Coverage     62.64%   62.65%           
- Complexity     2139     2141    +2     
=========================================
  Files           170      170           
  Lines          9882     9886    +4     
  Branches       1354     1355    +1     
=========================================
+ Hits           6191     6194    +3     
  Misses         3176     3176           
- Partials        515      516    +1     

Impacted Files	Coverage Δ
...rc/main/java/io/fabric8/maven/docker/StopMojo.java	44.34% <75.00%> (+1.10%)	⬆️

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

87.5% Coverage
0.0% Duplication