Refactor/simplify .travis.yml (#2090)
Refactor/simplify .travis.yml (#2090)

Over time, `.travis.yml` grew somewhat organically and became quite
complex. With some rewrites, it can set up the Travis CI stages
better, and become simpler, more logical, and more maintainable.

The refactoring keeps all existing functionality.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu
jerryscript-project/jerryscript,glistening/jerryscript,bsdelf/jerryscript,gabrielschulhof/jerryscript,dbatyai/jerryscript,grgustaf/jerryscript,akosthekiss/jerryscript,glistening/jerryscript,yichoi/jerryscript,robertsipka/jerryscript,akosthekiss/jerryscript,gabrielschulhof/jerryscript,bsdelf/jerryscript,zherczeg/jerryscript,glistening/jerryscript,bzsolt/jerryscript,bsdelf/jerryscript,bzsolt/jerryscript,bzsolt/jerryscript,yichoi/jerryscript,dbatyai/jerryscript,jerryscript-project/jerryscript,bsdelf/jerryscript,LaszloLango/jerryscript,akosthekiss/jerryscript,LaszloLango/jerryscript,dbatyai/jerryscript,grgustaf/jerryscript,akosthekiss/jerryscript,grgustaf/jerryscript,bzsolt/jerryscript,jerryscript-project/jerryscript,glistening/jerryscript,yichoi/jerryscript,gabrielschulhof/jerryscript,yichoi/jerryscript,akosthekiss/jerryscript,robertsipka/jerryscript,robertsipka/jerryscript,bzsolt/jerryscript,zherczeg/jerryscript,zherczeg/jerryscript,robertsipka/jerryscript,robertsipka/jerryscript,zherczeg/jerryscript,robertsipka/jerryscript,gabrielschulhof/jerryscript,grgustaf/jerryscript,jerryscript-project/jerryscript,glistening/jerryscript,glistening/jerryscript,grgustaf/jerryscript,dbatyai/jerryscript,jerryscript-project/jerryscript,zherczeg/jerryscript,LaszloLango/jerryscript,LaszloLango/jerryscript,bsdelf/jerryscript,grgustaf/jerryscript,dbatyai/jerryscript,bsdelf/jerryscript,gabrielschulhof/jerryscript,LaszloLango/jerryscript,yichoi/jerryscript