Set minimal length of Scan and Stop buttons to 6 characters

With English, the "Stop" and "Scan" buttons have the same numbers
of letters. Unfortunately with different translation it is different.
For example:
 - In Polish it is "Stop" and "Skanuj".
 - In Chinese is it "停止" and msgstr "扫描".

To do not have too small Scan/Stop button,
and to decrease Scan/Stop buttons size differency I have set minimal
Scan/Stop button length to 6 characters.
Status Job ID Name Coverage
  Test
passed #518439
build-arch

00:01:49

passed #518438
build-fedora

00:04:16

passed #518437
build-ubuntu

00:02:23