Rename TRAVIS_CI environment variable

[aesteve-rh]

The tests use TRAVIS_CI environment variable (e.g., in the broken_on_ci fixture) to determine if
we run in a CI, for tests that are expected to fail only in the pipeline run. Places where is used:

$ rg TRAVIS_CI                                                                                                                                                                                                                                        
tests/testValidation.py                                                                                                                                                                                                                                                                                                       
311:    To use on travis-ci, use name="TRAVIS_CI".  If a test is broken on both                                                                                                                                                                                                                                               
                                                                                                                                                                                                                                                                                                                              
tests/testing.py                                                                                                                                                                                                                                                                                                              
47:    return 'TRAVIS_CI' in os.environ                                                                                                                                                                                                                                                                                       

tests/network/nettestlib.py
509:    return 'TRAVIS_CI' in os.environ

tests/lib/protocoldetector_test.py
147:    @broken_on_ci("IPv6 not supported on travis", name="TRAVIS_CI")

tests/lib/yajsonrpc/stomprpcclient_test.py
138:    @broken_on_ci("Fails randomly in CI", name="TRAVIS_CI")
146:    @broken_on_ci("Fails randomly in CI", name="TRAVIS_CI")
158:    @broken_on_ci("Fails randomly in CI", name="TRAVIS_CI")
173:    @broken_on_ci("Fails randomly in CI", name="TRAVIS_CI")
214:    @broken_on_ci(reason="Fails randomly in CI", name="TRAVIS_CI")
232:    @broken_on_ci(reason="Fails randomly in CI", name="TRAVIS_CI")
276:    @broken_on_ci(reason="Fails randomly in CI", name="TRAVIS_CI")

tests/lib/yajsonrpc/stomp_test.py
85:        name="TRAVIS_CI")

tests/lib/yajsonrpc/jsonrpcserver_test.py
157:    @broken_on_ci(reason="Fails randomly in CI", name="TRAVIS_CI")
170:    @broken_on_ci("fails randomly in CI", name="TRAVIS_CI")
182:    @broken_on_ci("fails randomly in CI", name="TRAVIS_CI")
200:    @broken_on_ci("fails randomly in CI", name="TRAVIS_CI")
216:    @broken_on_ci("fails randomly in CI", name="TRAVIS_CI")
243:    @broken_on_ci("fails randomly in CI", name="TRAVIS_CI")
257:    @broken_on_ci("fails randomly in CI", name="TRAVIS_CI")
280:    @broken_on_ci("fails randomly in CI", name="TRAVIS_CI")

tests/storage/mount_test.py
141:    @broken_on_ci("mount check fails after successful mount", name="TRAVIS_CI")
152:    @broken_on_ci("mount check fails after successful mount", name="TRAVIS_CI")

tests/storage/filesd_test.py
148:        "OVIRT_CI" in os.environ or "TRAVIS_CI" in os.environ,

tests/container-shell
4:export TRAVIS_CI=1

tests/common/systemctl_test.py
36:    "OVIRT_CI" in os.environ or "TRAVIS_CI" in os.environ,

automation/check-patch.tests-container.environment.yaml
7: - name: 'TRAVIS_CI'

However, we do not run in Travis anymore, which makes the variable misleading.
We should rename the variable to avoid using Travis, to something such as RUN_ON_CI or OVIRT_CI, which is
more generic.

[nirs]

I think we can rename TRAVIS_CI to GITHUB_CI. All the OVIRT_CI checks are not relevant and likely can be removed.

Some of the TRAVIS_CI marks are also not relevant and can be removed, but not all. Some tests cannot run in containers so we cannot run them on github.

[aesteve-rh]

GITHUB_CI sounds good too, although we would run into the same issue if we ever move the repository hosting to a different one.