ProjectExplorer: Simplify use of AbstractProcessStep::init()

1. Systematically check for AbstractProcessStep::init() first in
   derived classes.
2. Use setupProcessParameters(processParameters()); by default in
   the base implementation.
3. Drop all re-implementations that are effectively the same.

Change-Id: I0ae54dd4909b354672a63ee56d0b7c2ea0732494
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/projectexplorer/abstractprocessstep.cpp

@@ -177,7 +177,12 @@ void AbstractProcessStep::setWorkingDirectoryProvider(const std::function<FilePa
 
 bool AbstractProcessStep::init()
 {
-    return !d->m_process;
+    if (d->m_process)
+        return false;
+
+    setupProcessParameters(processParameters());
+
+    return true;
 }
 
 void AbstractProcessStep::setupOutputFormatter(OutputFormatter *formatter)