[clock] use GTEST_SKIP in BuiltinNtpWithMiniChronydTest

Once switched to a newer version of gtest where GTEST_SKIP() is present,
it make sense to use GTEST_SKIP() instead of simple return to have
more accurate reports on passed/failed/skipped tests.

This is a follow-up to 78bd6c04ef37ca8906379a587140bc646433e28c.

Change-Id: I2b6fe6d8afb14e23a9f8b7766986b43040bfd7e9
Reviewed-on: http://gerrit.cloudera.org:8080/17587
Reviewed-by: Bankim Bhavsar <bankim@cloudera.com>
Tested-by: Kudu Jenkins
1 file changed