CI: build RPMs on CentOS, not Ubuntu

[weakcamel]

This is an extension of issue #29

• RPMs in Travis should be built on CentOS /Fedora and not on Ubuntu
• the path to install the package should be devised automatically, using something like:

%(%{__python} -c "from distutils.sysconfig import get_python_lib; import sys; sys.stdout.write(get_python_lib())")

Watch out for virtualenv though; we need the global path in there, not pointing to Virtualenv environment

Note:

# this is output on Ubuntu, on CentOS it would be site-packages

$ /usr/bin/python2  -c "from distutils.sysconfig import get_python_lib; import sys; sys.stdout.write(get_python_lib())"
/usr/lib/python2.7/dist-packages

$ . venv/bin/activate

$ python -c "from distutils.sysconfig import get_python_lib; import sys; sys.stdout.write(get_python_lib())"
/home/wmaleska/git/git-changelog-generator/venv/lib/python2.7/site-packages

[felfert]

Actually, I did build tests on several distros. See https://build.opensuse.org/package/show/home:felfert/gcg The existing packages (as of 0.2.0) did not build on any of the tested systems for various reasons:

• Build dependencies were missing in the .spec file resp. the .dsc file
• For some systems (mageia), several dependencies need to be named differently
• The version is unset in the spec file (In the travis build the cmdline is used to define %{version} which is normally a builtin variable that gets set by the Version: x.y.z directive

The above problems are fixed in my PR for python3 support

Regarding CentOS: It is impossible to provide an rpm for that, because all dependencies are missing. The only way to install on CentOS is with pip. On Mageia and OpenSuSE LEAP 15.1, I needed to provide my own dependencies of pythonX-semver and pythonX-jinja2

OBS (The OpenSuSE build service) is very nice for performing this kind of tests. It offers native builds on ~60 Linux distributions including other architectures like mips powerpc arm etc for free. There is also an interesting Feature: The actual build in a VM does not have network access. Instead, they parse the .spec/.dsc for dependencies and install those before they fire up the build process. This way, they make shure, that an RPM or DEB does properly define it's build dependencies and does not pull in something via pip or git or whatever means. The only issue: I have yet to find a way to automate copying of the travis build artifacts to them.