Source devtest_variables in tripleorc

In c31fdf3e76d215141d6a8f52361c279c9b933a10, overcloudrc was changed
to make use of the JSON data file to get the end-point and the
password, however, tripleorc doesn't know about TE_DATAFILE, which
leads to error messages when source'ing tripleorc and then overcloudrc
in a fresh environment.

Change-Id: I060be55f7d53c1252356edba6e3ebf38a5152708
Merge "Source devtest_variables in tripleorc"