A new "put" mode is added to the pk command, so that the "pk put"
command can be used to create and upload blobs.
What this command does is actually just call the previously named
"camput" executable, which is renamed to "pk-put" in this change.
This involves adding a new way to register a mode in cmdmain, when such
a mode is just meant to call an external binary. To emphasize the
distinction, the existing func (to register a sub-command, or a mode) is
renamed from RegisterCommand to RegisterMode, and RegisterCommand is now
the name of the new func/way.
Updates #981
Updates #1056
Change-Id: Ief954c17aa88a376f551df7de4b4e9fe41ad96d1
Brad Fitzpatrick