appliance: box commands for dumb bash in cleaning branch name, in build.sh

Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>
(cherry picked from commit edb5650c737d582595e134aab286e7304f299983)
Signed-off-by: Rohit Yadav <rohit.yadav@shapeblue.com>