Makefile: Add target to build check-programs

make check seems to be racy and requires -j 1. Building
check_PROGRAMS can however be -j 99.
Adding a make check-programs target to enable:
make -j 99 && make -j 99 check-programs && make -j 1 check
Also ammended .travis.yml to make use of this.

Signed-off-by: Andreas Fuchs <andreas.fuchs@sit.fraunhofer.de>
diff --git a/.travis.yml b/.travis.yml
index ac98a1d..e34a46c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -56,7 +56,8 @@
   - pushd ./build
   - ../configure --enable-unit --with-simulatorbin=$(pwd)/../ibmtpm/src/tpm_server
   - make -j$(nproc) distcheck
-  - make -j$(nproc) check
+  - make -j$(nproc) check-programs
+  - make -j1 check
   - cat test-suite.log
   - |
     for LOG in $(ls -1 test/unit/*.log); do