Fix heat-keystone-setup error when try to create heat user

Unset OS_SERVICE_TOKEN and OS_SERVICE_ENDPOINT temporarily to make
sure this command can run even if the OS_SERVICE_TOKEN and
OS_SERVICE_ENDPOIN exist in shell environment.
Remove die_if_not_set in get_data function, because there maybe no
data in get_data function, for example, if the heat user does not
exist, the die_if_not_set will be in error.
Remove die_if_not_set after keystone user-list for the same reason.

Change-Id: I132f975ac2da21e6ad7431ae326ad9bd538e4696
Closes-Bug: #1266670
Merge "Fix heat-keystone-setup error when try to create heat user"