[PATCH 4/4] travis-ci: set GIT_TEST_HTTPD in 'ci/lib-travisci.sh'

Commit 657343a60 (travis-ci: move Travis CI code into dedicated scripts, 2017-09-10) converted '.travis.yml's default 'before_install' scriptlet to the 'ci/install-dependencies.sh' script, and while doing so moved setting GIT_TEST_HTTPD=YesPlease for the 64-bit GCC and Clang Linux build jobs to that script. This is wrong for two reasons:

 - The purpose of that script is, as its name suggests, to install
   dependencies, not to set any environment variables influencing
   which tests should be run (though, arguably, this was already an
   issue with the original 'before_install' scriptlet).

 - Setting the variable has no effect anymore, because that script is
   run in a separate shell process, and the variable won't be visible
   in any of the other scripts, notably in 'ci/run-tests.sh'
   responsible for, well, running the tests.

Luckily, this didn't have a negative effect on our Travis CI build jobs, because GIT_TEST_HTTPD is a tri-state variable defaulting to "auto" and a functioning web server was installed in those Linux build jobs, so the httpd tests were run anyway.

Apparently the httpd tests run just fine without GIT_TEST_HTTPD being set, therefore we could simply remove this environment variable. However, if a bug were to creep in to change the Travis CI build environment to run the tests as root or to not install Apache, then the httpd tests would be skipped and the build job would still succeed. We would only notice if someone actually were to look through the build job's trace log; but who would look at the trace log of a successful build job?!

Since httpd tests are important, we do want to run them and we want to be loudly reminded if they can't be run. Therefore, move setting GIT_TEST_HTTPD=YesPlease for the 64-bit GCC and Clang Linux build jobs to 'ci/lib-travisci.sh' to ensure that the build job fails when the httpd tests can't be run. (We could set it in 'ci/run-tests.sh' just as well, but it's better to keep all environment variables in one place in 'ci/lib-travisci.sh'.)

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
---
 ci/install-dependencies.sh | 2 --
 ci/lib-travisci.sh         | 2 ++
 2 files changed, 2 insertions(+), 2 deletions(-)