libfdisk: return partno when add new partition

 * improve the way how sfdisk report results
 * the API change simplify applications

Signed-off-by: Karel Zak <kzak@redhat.com>
libfdisk: cleanup script size= code

Signed-off-by: Karel Zak <kzak@redhat.com>
sfdisk: improve UI

Signed-off-by: Karel Zak <kzak@redhat.com>
travis: whitelist branches

Signed-off-by: Karel Zak <kzak@redhat.com>