If the Luarocks version is lower than "v2.4.3", it does not support the "--only-deps" parameter. Even if we set the "--only-deps" parameter, no error message will be given during runtime.
We only wanted to install the dependencies in the deps directory, but the APISIX was also installed so that the test case might load the wrong version of the source code.
* travis: supports installing APISIX using the current branch and running
test cases separately in CI.
* bugfix: install apisix from local folder.
* travis: install `master` version apisix by luarocks and run e2e test.
