Do not require python-docker when RHEL > 7

RHEL 8 is not shipping python-docker, so we need to skip it as a
requirement in that case.

Change-Id: Ie5697dcff2fdeb1de4e66e25679b73494fc47908

openstack-tripleo-common.spec

@@ -59,7 +59,9 @@ BuildRequires:  python3-setuptools
 BuildRequires:  python3-devel
 BuildRequires:  python3-pbr
 BuildRequires:  python3-cryptography
+%if 0%{rhosp} == 1 && 0%{?rhel} < 8
 BuildRequires:  python3-docker
+%endif
 BuildRequires:  python3-GitPython
 BuildRequires:  python3-fixtures
 BuildRequires:  python3-glanceclient
@@ -102,7 +104,9 @@ Requires: python3-oslo-config >= 2:5.2.0
 Requires: python3-oslo-log >= 3.36.0
 Requires: python3-oslo-utils >= 3.33.0
 Requires: python3-six >= 1.10.0
+%if 0%{rhosp} == 1 && 0%{?rhel} < 8
 Requires: python3-docker >= 2.4.2
+%endif
 Requires: python3-passlib
 Requires: python3-keystoneauth1 >= 3.4.0
 Requires: python3-pbr >= 2.0.0