Address Valgrind issues in CI

Fixes "uninitialized values" errors reported by Valgrind. Problem
occurred from lack of specializations of googletest's PrintTo functions
for several custom types.

Tested:
On local CI container. After applying this patch issues stopped
appearing.

Change-Id: I98d9fd19724bee15add7b19422a9ddc2e4cbef09
Signed-off-by: Michal Orzel <michalx.orzel@intel.com>
diff --git a/tests/src/test_sensor_cache.cpp b/tests/src/test_sensor_cache.cpp
index 218e160..3d12563 100644
--- a/tests/src/test_sensor_cache.cpp
+++ b/tests/src/test_sensor_cache.cpp
@@ -21,6 +21,11 @@
         service(service), path(path)
     {}
 
+    friend void PrintTo(const IdParam& param, std::ostream* os)
+    {
+        *os << "(" << param.service << "): " << param.path;
+    }
+
     std::string service;
     std::string path;
 };