meson: Add googletest as a subproject

Allow the tests to build without requiring a system-wide installation of
googletest.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: Iaf685cd1886672a435ba66c4aae3a0772b714dd5
diff --git a/test/meson.build b/test/meson.build
index 74bb079..4aaaeea 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -11,9 +11,7 @@
 else
   dynamic_linker = []
 endif
-gmock = dependency('gmock', disabler: true, required: build_tests)
-gtest = dependency('gtest', main: true, disabler: true, required: build_tests)
-dependecy_list = [gtest, gmock, sdbusplus, phosphor_logging, phosphor_dbus_interfaces]
+dependecy_list = [gtest_dep, gmock_dep, sdbusplus, phosphor_logging, phosphor_dbus_interfaces]
 
 configuration_inc = include_directories('..', '../vpd-manager', 'vpd-manager-test', '../vpd-parser')