Fix a way to handle CLASSPATH environment variable

You must replace an entry not but just append it because it's ignored at specfic platform like Windows.
Gradle's wrapper stream writes nothing to console

It seems very similar to https://github.com/kobo/groovyserv/issues/52
Support running on cygwin with JAVA_HOME
Time out while waiting for server startup
Stop a next build task if executeCommand is failed
Fix ExecScriptSpec to be passed on Windows
Fix a test frozen caused by exceeding a process output buffer
Fix a ignored test case because of lack of a Spock's label