Fix cta_valgrind error

[----------] 1 test from cta_taped
[ RUN      ] cta_taped.InvocationTests
/builds/cta/CTA/build_rpm/RPM/BUILD/cta-4-4629058gite6ecdac0/tapeserver/cta-tapedSystemtests.cpp:61: Failure
Expected: (std::string::npos) != (spNoDrive.stdout().find("MSG=\"Aborting cta-taped on uncaught exception. Stack trace follows.\" Message=\"No drive found in configuration\"")), actual: 18446744073709551615 vs 18446744073709551615
[  FAILED  ] cta_taped.InvocationTests (1176 ms)