New package: py-mysql-connector (#10327)

* New package: py-mysql-connector

* Fixed docstring

* 1. Determined that py-setuptools was not needed at all, so removed.
2. Added py-protobuf.  Docs seem to imply that only C protobuf library is required; however, the Python setup.py says differently, and some Python code seems to reference protobuf too.  I don't know why this worked for me, but it looks like including py-protobuf is the right thing to do.

* Applied solution detailed in:

https://github.com/mysql/mysql-connector-python/pull/9

Uncommenting this patch will make `error: option --single-version-externally-managed not recognized`  reappear.

* Clean up / reorder lines

* flake8

var/spack/repos/builtin/packages/py-mysql-connector/package.py

@@ -0,0 +1,26 @@
+# 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 PyMysqlConnector(PythonPackage):
+    """MySQL Connector/Python is implementing the MySQL Client/Server
+    protocol completely in Python. No MySQL libraries are needed, and
+    no compilation is necessary to run this Python DB API v2.0
+    compliant driver."""
+
+    homepage = "https://github.com/mysql/mysql-connector-python"
+    url      = "https://github.com/mysql/mysql-connector-python/archive/8.0.13.tar.gz"
+    git      = "https://github.com/mysql/mysql-connector-python.git"
+
+    version('8.0.13', sha256='d4c0834c583cdb90c0aeae90b1917d58355a4bf9b0266c16fd58874a5607f9d4')
+
+    # Fix `error: option --single-version-externally-managed not recognized`
+    # https://github.com/mysql/mysql-connector-python/pull/9
+    patch('single-version.patch')
+
+    depends_on('py-setuptools', type=('build', 'run'))
+    depends_on('py-protobuf@3.0.0:', type=('build', 'run'))

var/spack/repos/builtin/packages/py-mysql-connector/single-version.patch

@@ -0,0 +1,22 @@
+diff --git a/lib/cpy_distutils.py b/lib/cpy_distutils.py
+index a9132e5..3cffee6 100644
+--- a/lib/cpy_distutils.py
++++ b/lib/cpy_distutils.py
+@@ -29,9 +29,14 @@
+ """Implements the DistUtils command 'build_ext'
+ """
+ 
+-from distutils.command.build_ext import build_ext
+-from distutils.command.install import install
+-from distutils.command.install_lib import install_lib
++try:
++    from setuptools.command.build_ext import build_ext
++    from setuptools.command.install import install
++    from setuptools.command.install_lib import install_lib
++except ImportError:
++    from distutils.command.build_ext import build_ext
++    from distutils.command.install import install
++    from distutils.command.install_lib import install_lib
+ from distutils.errors import DistutilsExecError
+ from distutils.util import get_platform
+ from distutils.version import LooseVersion