qbs build: Add convenience function for reading process output.

Change-Id: I998ec20de032b59448585c851e79912010cdac08
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

qbs/imports/QtcProcessOutputReader/procoutputreader.js

@@ -0,0 +1,11 @@
+var Process = loadExtension("qbs.Process")
+
+function readOutput(executable, args)
+{
+    var p = new Process();
+    var output = "";
+    if (p.exec(executable, args, false) !== -1)
+        output = p.readStdOut().trim(); // Trailing newline.
+    p.close();
+    return output;
+}