cppcheck : Add googletest library while running cppcheck

- cppcheck shows a syntaxerror while parsing TEST & TEST_F
  macros in the repo's test files, as cppcheck cannot understand
  how a TEST or a TEST_F works.

 Example:
 When repo specific CI is run on phosphor-networkd, it throws following
 errors:

 test/test_ethernet_interface.cpp:108:1: error: syntax error [syntaxError]
 TEST_F(TestEthernetInterface, NoIPaddress)
 ^
 test/test_neighbor.cpp:35:1: error: syntax error [syntaxError]
 TEST(ParseNeighbor, SmallMsg)
 ^

- This commit would load googletest.cfg that contains information
  about google test types and functions. With such information
  Cppcheck understands the code better and therefore get better
  results.

TestedBy:

- Had run docker CI against the networkd, and the above mentioned errors
  are gone.

Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
Change-Id: If72edd4e734fb201e8a2a937fdfe8bc62dfb5f4b
diff --git a/scripts/unit-test.py b/scripts/unit-test.py
index 3d12fe5..d6662c1 100755
--- a/scripts/unit-test.py
+++ b/scripts/unit-test.py
@@ -375,7 +375,7 @@
 
     # http://cppcheck.sourceforge.net/manual.pdf
     params = ['cppcheck', '-j', str(multiprocessing.cpu_count()),
-              '--enable=all', '--file-list=-']
+              '--enable=all', '--library=googletest', '--file-list=-']
 
     cppcheck_process = subprocess.Popen(
         params,