travis-ci: Emulate 'make tests'

The 'tests' target will run sandbox, sandbox_spl and sandbox_flattree in
test.py and in the case of sandbox_spl ensure that we just run the
specific tests for that build.  Update our matrix to perform similar
test.py runs.

Signed-off-by: Tom Rini <trini@konsulko.com>

.travis.yml

@@ -264,6 +264,15 @@ matrix:
           BUILDMAN="^sandbox$"
           TOOLCHAIN="x86_64"
     - env:
+        - TEST_PY_BD="sandbox_spl"
+          TEST_PY_TEST_SPEC="test_ofplatdata"
+          BUILDMAN="^sandbox$"
+          TOOLCHAIN="x86_64"
+    - env:
+        - TEST_PY_BD="sandbox_flattree"
+          BUILDMAN="^sandbox_flattree$"
+          TOOLCHAIN="x86_64"
+    - env:
         - TEST_PY_BD="vexpress_ca15_tc2"
           TEST_PY_ID="--id qemu"
           QEMU_TARGET="arm-softmmu"