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
1 file changed