Reduce libcudf memcheck tests output

[davidwendt]

Uses the GTEST_BRIEF=1 environment variable to reduce the output of the memcheck script.
This should help find errors more quickly in the nightly memcheck build output.

Example output where 1 test fails in the entire STRINGS_TEST

$ export GTEST_BRIEF=1
$ gtests/STRINGS_TEST 
/cudf/cpp/tests/utilities/column_utilities.cu:566: Failure
Failed
first difference: lhs[12] = 50089, rhs[12] = 500890
Google Test trace:
/cudf/cpp/tests/strings/attrs_tests.cpp:45:  <--  line of failure

[  FAILED  ] StringsAttributesTest.CodePoints (13 ms)
[==========] 488 tests from 53 test suites ran. (697 ms total)
[  PASSED  ] 487 tests.

It reports only on failing tests.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[davidwendt]

/merge