Add possibility to specify dcosAuthToken file

[sjahreis]

Overwrite dcosAuthToken(void) with dcosAuthToken(File).

[toplac]

This would solve the following issue when running gradle using cygwin on Windows:

./gradlew deployAll --stacktrace results in the following Exception:

Caused by: java.io.FileNotFoundException: C:\Users\t.placht\.dcos\dcos.toml (Das System kann den angegebenen Pfad nicht finden)

The problem is System.getProperty("user.home") returns a path specified in the Windows registry and not the Cygwin home folder.
As a a workaround it is possible to use:

./gradlew deployAll -Duser.home=$HOME