MavenIntegrator shall not add arguments if they are already present in original command

This applies to:

• build phases
• Clover's properties

Current problems:

1) The "clean" phase can be doubled

For example if original command has:

mvn clean test

it becomes:

mvn clean clean clover2:setup test clover2:aggregate clover2:clover ...

2) User cannot override default values of Clover properties

For example if a property is already defined:

mvn test -Dmaven.clover.licenseLocation=/my/clover.license

MavenIntegrator adds a second one with it's own value:

mvn test -Dmaven.clover.licenseLocation=/my/clover.license -Dmaven.clover.licenseLocation=/tmp/clover.license