kas-docker: switch to /bin/bash as SHELL per default

In case SHELL is `/usr/bin/bash`, `/usr/bin/zsh` or something else that
is not available in the kas docker container, fall back to `/bin/bash`.

Signed-off-by: Claudius Heine <ch@denx.de>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas-docker

@@ -263,6 +263,9 @@ case "$SHELL" in
 /bin/sh|/bin/bash|/bin/dash)
 	set -- "$@" -e "SHELL=$SHELL"
 	;;
+*)
+	set -- "$@" -e "SHELL=/bin/bash"
+	;;
 esac
 
 if [ -z "${NO_PROXY_FROM_ENV+x}" ]; then