cmake: disable VTA for osdcap.cc

cmake: disable VTA for osdcap.cc

this silences the warning of:
```
In file included from
/home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/include/gtest/gtest.h:58:0,
                 from
/home/jenkins-build/build/workspace/ceph-pull-requests/src/test/osd/osdcap.cc:20:
/home/jenkins-build/build/workspace/ceph-pull-requests/src/test/osd/osdcap.cc:
In member function ‘virtual void
OSDCap_AllowClassMulti_Test::TestBody()’:
/home/jenkins-build/build/workspace/ceph-pull-requests/src/test/osd/osdcap.cc:766:6:
note: variable tracking size limit exceeded with
-fvar-tracking-assignments, retrying without
 TEST(OSDCap, AllowClassMulti) {
      ^
/home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/include/gtest/internal/gtest-internal.h:1211:3:
note: in definition of macro ‘GTEST_TEST_CLASS_NAME_’
   test_case_name##_##test_name##_Test
   ^
/home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/include/gtest/gtest.h:2181:3:
note: in expansion of macro ‘GTEST_TEST_’
   GTEST_TEST_(test_case_name, test_name, \
   ^
/home/jenkins-build/build/workspace/ceph-pull-requests/src/googletest/googletest/include/gtest/gtest.h:2187:42:
note: in expansion of macro ‘GTEST_TEST’
 # define TEST(test_case_name, test_name) GTEST_TEST(test_case_name,
 # test_name)
                                          ^
/home/jenkins-build/build/workspace/ceph-pull-requests/src/test/osd/osdcap.cc:766:1:
note: in expansion of macro ‘TEST’
 TEST(OSDCap, AllowClassMulti) {
 ^
```

see also b668051

Signed-off-by: Kefu Chai <kchai@redhat.com>