Add Travis CI badge for gap-docker-master-testsuite

[olexandr-konovalov]

This PR adds new Travis CI badge which points to the Travis build at https://travis-ci.org/gap-system/gap-docker-master-testsuite.

This build allows everyone (not only to those who can access Jenkins instance in St Andrews) to see how tests from testinstall, teststandard and testbugfix directories behave in three scenarios: with no packages, with default packages, and with all packages loaded.

This build is a Travis CI cron job, scheduled to run daily, and it uses the GAP Docker container for the master branch (https://hub.docker.com/r/gapsystem/gap-docker-master/), which is also built daily, with packages from the http://www.gap-system.org/pub/gap/gap4pkgs/packages-master.tar.gz archive, which is updated periodically when package updates pass some internal checks in Jenkins.

Adding this badge will allow others to see the current status of the test and easily find test logs.

At the moment, tests which are failing are those reported in #1849 and #1860.

[codecov]

Codecov Report

Merging #1881 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1881      +/-   ##
==========================================
+ Coverage   63.49%   63.49%   +<.01%     
==========================================
  Files         952      952              
  Lines      286804   286803       -1     
  Branches    12722    12722              
==========================================
+ Hits       182109   182110       +1     
+ Misses     101899   101896       -3     
- Partials     2796     2797       +1

Impacted Files	Coverage Δ
src/iostream.c	46.24% <0%> (-0.4%)	⬇️
src/hpc/traverse.c	77.99% <0%> (-0.39%)	⬇️
src/stats.c	79.15% <0%> (-0.14%)	⬇️
src/gap.c	60.4% <0%> (-0.09%)	⬇️
src/lists.c	56.71% <0%> (+0.11%)	⬆️
src/funcs.c	74.89% <0%> (+0.14%)	⬆️
src/hpc/threadapi.c	34.49% <0%> (+0.18%)	⬆️
hpcgap/pkg/gapdoc/PackageInfo.g	35.22% <0%> (+0.22%)	⬆️
hpcgap/lib/hpc/stdtasks.g	38.87% <0%> (+0.25%)	⬆️

[fingolfin]

I am unhappy that this makes two visually indistinguishable Travis badges appear. And worse, both have the same alt string "Build Status" -- so the only way to find out which is which is to check the URLs.

So the first change should be to use different "alt" strings, say "Build status" or "master branch status", versus e.g. "Docker build status".

Secondly, I'd strongly prefer if there also was an immediate visible clue as to which badge is is which. I don't know if the Travis badges allow that, but https://shields.io certainly does (and according to this blog post they are the source of Travis badges anyway?):

• Default shield for gap-system/gap:
• Shield with custom label:

There are other options (e.g. to adjust colors, styling etc.), describe on their homepage.

[olexandr-konovalov]

Closing in favour of https://github.com/gap-system/gap-distribution - I've put a collection of badges there, where they will be less confusing.