Added redis-server to file

The goal is to add packages that are ignored by travis as suggested in pull request #4112 by dannyroberts.
Added TRAVIS_INSTALL="y" global variable

This global variable is read by install.sh so variables with #[travis_ignore] are ignored in the requirements/apt-packages.txt.
Added TRAVIS_INSTALL if statement to ignore [travis_ignore] packages

The goal of this change is to have travis ignore the redis-server in requirements/apt-packages.txt which is marked with #[travis_ignore]. The grep -v command gets everything in the text file except those that contain [travis_ignore] in the line. The TRAVIS_INSTALL variable is set in travis.yml. If it's not a travis install ($TRAVIS_INSTALL != "y"), then the redis-server is read in and installed.
Merge pull request #4124 from craigappl/Add_redis-server_and_travis_ignore]

Add redis-server and [travis_ignore]