add travis ci support

[fengggli]

1. travis only supports Ubuntu 14.04 system. I use a workaround to test build in a 1604 docker image.
2. I am using a slightly modified docker image, the Dockerfile contains the details
3. In the travis scirpt, I have disabled the self test for google benchmark, the cxx+03 test got confused in auto-build process.
4. add compiler check in examples/, this is related to issue 8 (compile option -fdump-class-hierarchy incompatible with clang++ #8)
5. make -j in rocksdb will exhaust the memory in traivis. I make job number to 2 (only for travis auto-build).
6. even rocksdb is built, it's not found by comanche-rockstore , see the detailed build history. I have to disable the rockstore temporarily.
7. update the apt-install scripts
8. now requires cmake 3.6, since google benchmark needs the FILTER feature , see build history