travis-ci: Added minimal travis job

Added an additional job to the CI matrix which does a minimal UPM
build (only C, C++, and unit tests) which can run and pass/fail quickly.

Signed-off-by: Noel Eck <noel.eck@intel.com>

.travis.yml

@@ -14,6 +14,13 @@ jobs:
   allow_failures:
     - env: TARGET=ipk
   include:
+    - &run-with-clang-minimal
+      stage: Clang 3.8 - minimal with unit tests
+      env: TARGET=minimal
+      before_script: docker-compose pull ${TARGET}
+      script:
+        - export CC=clang-3.8 CXX=clang++-3.8
+        - BUILDARCH=MOCK docker-compose run ${TARGET}
     - &run-with-clang
       stage: Clang 3.8
       env: TARGET=python