Start to deprecate Python 2 and 3.5

Python 2 will reach EOL in 18 months. Start to issue deprecation
warnings on Python 2.

No longer claim support for Python 3.5. Python 3.5 is untested.

NOTE: At first I tried to raise the deprecation warning from
ipalib.__init__. This caused some unforseen side-effects with
ipaplatform namespace package on Python 2. Eventually it was easier to
raise the deprecation warning in ipaplatform. RHEL and Debian platforms
don't raise the deprecation warning yet, because they use Python 2.

Fixes: https://pagure.io/freeipa/issue/7568
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Tibor Dudlak <tdudlak@redhat.com>

ipaplatform/fedora/__init__.py

@@ -20,4 +20,14 @@
 '''
 This module contains Fedora specific platform files.
 '''
+import sys
+import warnings
+
 NAME = 'fedora'
+
+if sys.version_info < (3, 6):
+    warnings.warn(
+        "Support for Python 2.7 and 3.5 is deprecated. Python version "
+        "3.6 or newer will be required in the next major release.",
+        category=DeprecationWarning
+    )

ipasetup.py.in

@@ -97,7 +97,7 @@ common_args = dict(
     url="https://www.freeipa.org/",
     download_url="https://www.freeipa.org/page/Downloads",
     platforms=["Linux"],
-    python_requires=">=2.7.5,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*",
+    python_requires=">=2.7.5,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*",
     classifiers=[
         "Development Status :: 5 - Production/Stable",
         "Intended Audience :: System Administrators",
@@ -107,7 +107,6 @@ common_args = dict(
         "Programming Language :: Python :: 2",
         "Programming Language :: Python :: 2.7",
         "Programming Language :: Python :: 3",
-        "Programming Language :: Python :: 3.5",
         "Programming Language :: Python :: 3.6",
         "Programming Language :: Python :: Implementation :: CPython",
         "Operating System :: POSIX",