I would be very surprised if we didn't have a name for this bean in English, but living outside of the U.S., I'm not able to skim the supermarket shelves to find the English name first-hand. Here in Italy we have a bean that matches your description perfectly; In Italian it is called "borlotto" or "fagiolo borlotto". (The borlotto is not a dwarf bean, however.)

Apparently your bean is - according to the Nouveau Petit Le Robert: "harcots nains à écosser".
In the Hachette Dictionnaire de langue francaise, under the subheading "Haricots nains", the following beans are listed: "soissons nain, flageolet, suisse rouge, marbré nain". In English, the equivalent of "haricot nain" is "dwarf bean". According Elsevier's Dictionary of Plant Names, there is actually a bean called a "dwarf bean" in English. Other names listed for this bean are "(Phaseolus vulgaris), French bean, small kidney bean, kidney bean, flageolet, common bean, haricot bean , navy bean". The French beans listed under Phaseolus vulgaris are "haricot commun; haricot; faséole; flageolet;" There is also a bean called the "bush kidney bean" (Phaseolus vulgaris humilis), for which there is no French equivalent listed, which is also a type of dwarf bean. Unfortunately I don't have an exact answer for you, but hopefully my answer will lead you to more information.
Very best regards,
Andréa