Move try_umount above cleanup()
try_umount() replaced all umount calls in PR #264.
Unfortunately, the function is defined too late for a few of functions,
especially for cleanup(), which fails with:
-> Failed (rc=1)
/sbin/grml-debootstrap: line 260: try_umount: command not found
Unexpected non-zero exit code 127 in /sbin/grml-debootstrap /sbin/grml-debootstrap /sbin/grml-debootstrap /sbin/grml-debootstrap /sbin/grml-debootstrap at line 260 329 1107 1179 0 detected!
last bash command: try_umount 3 "${MNTPOINT}"/boot/efi
-> Failed (rc=1)
/sbin/grml-debootstrap: line 260: try_umount: command not found
Moved the try_umount above cleanup().
Closes: #271