Make all testing shell scripts executable

The shell scripts need to have the execute bit set (chmod +x foo.sh) in
order to be runnable on Linux. When running the development VMs on a
Windows host, this problem will not manifest, because the permissions of
a VirtualBox shared folder are 0777 (rwxrwxrwx) in the guest, since the
backing NTFS filesystem doesn't share the Linux permissions model. But
when running the VM on a Linux host (such as the build server that we'll
eventually be running the tests on), the permissions on the vboxsf share
will match the permissions of the backing filesystem, and so the shell
scripts need to be set to chmod +x explicitly.