roles: bifrost-ironic-install: Add PyMySQL dependency for ironic-dbsync

We are using MariaDB database for ironic so we need to install
the optional PyMySQL dependency for sqlalchemy on all distributions
otherwise ironic-dbsync fails with the following error:

CRITI [ironic] ImportError: No module named pymysql
Traceback (most recent call last):
  File "/usr/bin/ironic-dbsync", line 10, in <module>
    sys.exit(main())
  File "/usr/lib/python2.7/site-packages/ironic/cmd/dbsync.py", line 103, in main
    CONF.command.func()
  File "/usr/lib/python2.7/site-packages/ironic/cmd/dbsync.py", line 35, in upgrade
     migration.upgrade(CONF.command.revision)
  File "/usr/lib/python2.7/site-packages/ironic/db/migration.py", line 36, in upgrade
     return get_backend().upgrade(version)
  File "/usr/lib/python2.7/site-packages/ironic/db/sqlalchemy/migration.py", line 56, in upgrade
     alembic.command.upgrade(config, revision or 'head')
  [...]
  File "/usr/lib64/python2.7/site-packages/sqlalchemy/dialects/mysql/pymysql.py", line 49, in dbapi
     return __import__('pymysql')
ImportError: No module named pymysql

Change-Id: Ib44779de06a7bad91a08e148e1c0e1eb9815afe8

playbooks/roles/bifrost-ironic-install/defaults/required_defaults_Suse_family.yml

@@ -47,4 +47,5 @@ required_packages:
   - socat
   - python-pip
   - gcc
+  - python-PyMySQL
 iscsi_client_package: "open-iscsi"

playbooks/roles/bifrost-ironic-install/tasks/install.yml

@@ -85,6 +85,16 @@
 - name: "Install pymysql in venv if using"
   include: pip_install.yml package=pymysql virtualenv=bifrost_venv_dir
   when: skip_install is not defined and (enable_venv | bool == true)
+# NOTE(hwoarang): The python-pymysql package is not available on the CentOS7
+# and old Debian/Ubuntu repositories so we need to get it via pip
+- name: "Install pymysql on CentOS/Ubuntu if necessary"
+  include: pip_install.yml package=pymysql
+  when:
+    - skip_install is not defined
+    - enable_venv | bool == false
+    - (ansible_distribution == 'CentOS' and ansible_distribution_major_version <= 7) or
+      (ansible_distribution == 'Ubuntu' and ansible_distribution_version|version_compare('14.10', '=='))
+
 - name: "Install Ironic using pip"
   include: pip_install.yml
     package=ironic