CBD-935:  better usage() statement

Change-Id: I859883dc032024d2de856c93026fe98cfdc99ac5
CBD-935:  add optional -P <platform> arg, appended to email subject
          add DO_SENDIT flag, on by default.  Set to zero to suppress.

Change-Id: I563e7ac2d5f5905c84bafadbf655a15b2f271052
CBD-935:  replace DO_SENDIT env.var. with -e <flag_value> argument.
          Use " -e 0" (zero) to suppress sending email.

Change-Id: Ib0c07cc8718fe070274faf80f4e2f258b1ba04af