Move libpldm test cases into libpldm directory

The test cases for different libraries in this repo are put in the same
test directory.
As a follow up of building libpldm only, move the test cases of libpldm
into libpldm/tests, so that the test cases could be built and run by
libpldm-only option.

Tested: Verify the libpldm tests are built and run by libpldm-only
        option.
        Verify all the tests are built and run without libpldm-only
        option.

Signed-off-by: Lei YU <mine260309@gmail.com>
Change-Id: I097000bef316f787ef1894f1a3feec5089ea081a
diff --git a/.gitignore b/.gitignore
index 012f3f9..8d31869 100644
--- a/.gitignore
+++ b/.gitignore
@@ -71,6 +71,7 @@
 /test/*.gcda
 /test/*.gcno
 /test/vgcore.*
+/libpldm/tests/vgcore.*
 /test/libpldm_base_test
 /test/libpldmresponder_base_test
 /test/libpldm_bios_test