New Package: py-pyside2 (#13647)

* New Package: py-pyside2

https://wiki.qt.io/Qt_for_Python

The Qt for Python project aims to provide a complete port of the PySide module
to Qt 5. The development started on GitHub in May 2015. The project managed to
port Pyside to Qt 5.3, 5.4 & 5.5. During April 2016 The Qt Company decided to
properly support the por

* Address review comments:

+ Add a variant for `+doc` and only depned on some packages if this variant is
  active.
+ Enable building the tests if requested.
+ Correct registered required verions for python and qt.

* Remove dead code, fix depends_on command args.

* fix one more flake8 issue.

* One more fix to  arguments and change  version name to .

var/spack/repos/builtin/packages/py-pyside2/package.py

@@ -0,0 +1,53 @@
+# Copyright 2013-2019 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class PyPyside2(PythonPackage):
+    """Python bindings for Qt."""
+    homepage = "https://pypi.org/project/PySide2/"
+    url      = "https://code.qt.io/pyside/pyside-setup.git"
+    git      = "https://code.qt.io/pyside/pyside-setup.git"
+
+    # More recent versions of PySide2 (for Qt5) have been taken under
+    # the offical Qt umbrella.  For more information, see:
+    # http://wiki.qt.io/Qt_for_Python_Development_Getting_Started
+
+    version('develop', tag='dev')
+    version('5.13.2', tag='v5.13.2', submodules=True)
+    version('5.13.1', tag='v5.13.1', submodules=True)
+    version('5.13.0', tag='v5.13.0', submodules=True)
+    version('5.12.5', tag='v5.12.5', submodules=True)
+
+    variant('doc', default=False, description='Enables the generation of html and man page documentation')
+
+    depends_on('python@2.7:2.7.99,3.5.0:3.5.99,3.6.1:', type=('build', 'run'))
+
+    depends_on('cmake@3.1:', type='build')
+    depends_on('llvm@6:', type='build')
+    depends_on('py-setuptools', type='build')
+    depends_on('py-wheel', type='build')
+    depends_on('qt@5.11:+opengl', type=('build', 'run'))
+
+    depends_on('graphviz', when='+doc', type='build')
+    depends_on('libxml2@2.6.32:', when='+doc', type='build')
+    depends_on('libxslt@1.1.19:', when='+doc', type='build')
+    depends_on('py-sphinx', when='+doc', type='build')
+
+    def build_args(self, spec, prefix):
+        args = [
+            '--parallel={0}'.format(make_jobs),
+            '--ignore-git',
+            '--qmake={0}'.format(spec['qt'].prefix.bin.qmake)
+        ]
+        if self.run_tests:
+            args.append('--build-tests')
+        return args
+
+    @run_after('build')
+    def build_docs(self):
+        if '+doc' in self.spec:
+            make('apidoc')