[partition] Implement other way of getting partitions

- Just read /proc/partitions and process it; split into columns,
   add relevant bits.
 - This implementation supports devices named "name", which the other
   didn't (but that would be really weird).

The tests now pass.

src/modules/partition/tests/ClearMountsJobTests.cpp

@@ -34,6 +34,28 @@ getPartitionsForDevice_other(const QString& deviceName)
 {
     QStringList partitions;
 
+    QFile dev_partitions( "/proc/partitions" );
+    if ( dev_partitions.open( QFile::ReadOnly ) )
+    {
+        cDebug() << "Reading from" << dev_partitions.fileName();
+        QTextStream in( &dev_partitions );
+        (void) in.readLine();  // That's the header line, skip it
+        while ( !in.atEnd() )
+        {
+            // The fourth column (index from 0, so index 3) is the name of the device;
+            // keep it if it is followed by something.
+            QStringList columns = in.readLine().split( ' ', QString::SkipEmptyParts );
+            if ( ( columns.count() >= 4 ) && ( columns[3].startsWith( deviceName ) )  && ( columns[3] != deviceName ) )
+            {
+                partitions.append( columns[3] );
+            }
+        }
+    }
+    else
+    {
+        cDebug() << "Could not open" << dev_partitions.fileName();
+    }
+
     return partitions;
 }