qemuMigrationSrcRun: Sanitize setting of cookieFlags and migrate_flags on storage migration
qemuMigrationSrcRun: Sanitize setting of cookieFlags and migrate_flags on storage migration

Base the decision on the main API flags (VIR_MIGRATE_NON_SHARED_DISK,
QEMU_MONITOR_MIGRATE_NON_SHARED_INC) via a boolean 'storageMigration'
rather than juggling everything trhough 'migration_flags'.

After this patch 'migration_flags' is updated to contain the legacy
storage migration flags only when we'll be about to use it rather than
setting it and then resetting it.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Tested-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>
Reviewed-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

jfehlig/libvirt,libvirt/libvirt,zippy2/libvirt,nertpinx/libvirt,nertpinx/libvirt,libvirt/libvirt,nertpinx/libvirt,nertpinx/libvirt,libvirt/libvirt,jfehlig/libvirt,zippy2/libvirt,jfehlig/libvirt,olafhering/libvirt,libvirt/libvirt,olafhering/libvirt,jfehlig/libvirt,olafhering/libvirt,crobinso/libvirt,crobinso/libvirt,crobinso/libvirt,zippy2/libvirt,zippy2/libvirt,olafhering/libvirt,nertpinx/libvirt,crobinso/libvirt