[partition] Set FlagBoot for the root partition

- This only applies to legacy (non-EFI) BIOS systems, and
   adds the FlagBoot to whatever is already set for the root
   filesystem, and only when autopartitioning the device.

Submitted by aliveafter1000.

FIXES: #1046
CLOSES: #1049

src/modules/partition/core/PartitionActions.cpp

@@ -223,7 +223,11 @@ doAutopartition( PartitionCoreModule* core, Device* dev, const QString& luksPass
     }
     PartitionInfo::setFormat( rootPartition, true );
     PartitionInfo::setMountPoint( rootPartition, "/" );
-    core->createPartition( dev, rootPartition );
+    // Some buggy (legacy) BIOSes test if the bootflag of at least one partition is set.
+    // Otherwise they ignore the device in boot-order, so add it here.
+    core->createPartition( dev, rootPartition,
+                           rootPartition->activeFlags() | ( isEfi ? PartitionTable::FlagNone : PartitionTable::FlagBoot )
+                         );
 
     if ( shouldCreateSwap )
     {