gtest: Test presence of source on existing file

gtest: Test presence of source on existing file

configure is not in upstream's repo
because, it's intended to be generated from configure.ac.

So to avoid ambiguity, we test if CMake file is present instead.

Bug: https://jira.iotivity.org/browse/IOT-1745
Change-Id: Ia2e7c8c4d0c827b300b9345c9cb7811a193cfd9e
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/17855
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Mats Wichmann <mats@linux.com>
Reviewed-by: Ashok Babu Channa <ashok.channa@samsung.com>