rfc.sh: Include BUG: header even in first run

Set the commit hook before entiring editor mode. This fixes the
error where rfc.sh after first clone does not set BUG: header

Change-Id: Ic0e9f2d3f656bc81e29d35556022fbdff2f61225
BUG: 764890
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/5632