.travis.yml: Cache acceptance-test assets

Keep all acceptance-test assets in the same cache bucket.

As of v5.0.0-rc1, the cache is 2610.11MB:
https://travis-ci.org/github/philmd/qemu/jobs/670558103

Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200403172919.24621-6-philmd@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
diff --git a/.travis.yml b/.travis.yml
index e0c7221..2fd63ec 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -318,8 +318,10 @@
       env:
         - CONFIG="--enable-tools --target-list=aarch64-softmmu,alpha-softmmu,arm-softmmu,m68k-softmmu,microblaze-softmmu,mips-softmmu,mips64el-softmmu,nios2-softmmu,or1k-softmmu,ppc-softmmu,ppc64-softmmu,s390x-softmmu,sparc-softmmu,x86_64-softmmu,xtensa-softmmu"
         - TEST_CMD="make check-acceptance"
+        - CACHE_NAME="${TRAVIS_BRANCH}-linux-gcc-acceptance"
       after_script:
         - python3 -c 'import json; r = json.load(open("tests/results/latest/results.json")); [print(t["logfile"]) for t in r["tests"] if t["status"] not in ("PASS", "SKIP")]' | xargs cat
+        - du -chs $HOME/avocado/data/cache
       addons:
         apt:
           packages: