Process: Use more rawStd{Out,Err} const methods instead of mutable ones

Avoid using readAllStandard{Output,Error} mutable methods if possible.
Use non-mutable methods when we are not connected to
readyReadStandard{Output,Error} signals.

Change-Id: I2e830e571b9eab2177fd856bbe06dfc5137d9c01
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/gitlab/queryrunner.cpp

@@ -110,7 +110,7 @@ QueryRunner::QueryRunner(const Query &query, const Id &id, QObject *parent)
             }
             VcsBase::VcsOutputWindow::appendError(m_process.exitMessage());
         } else {
-            emit resultRetrieved(m_process.readAllRawStandardOutput());
+            emit resultRetrieved(m_process.rawStdOut());
         }
         emit finished();
     });