Add binary_prefix=true argument to mysql uri

This patch adds the argument binary_prefix=true to MySQL uri if
OpenStack version is equal or greater than Rocky due to Python
upper-constraints [1]. This argument is required because of PyMySQL's
change from version 0.8 and on [2], in order to fix Gnocchi API
warnings like this [3].

[1] https://github.com/openstack/requirements/blob/stable/rocky/upper-constraints.txt#L377
[2] https://github.com/PyMySQL/PyMySQL/blob/master/CHANGELOG#L61-L64
[3] gnocchixyz/gnocchi#847

Change-Id: Ie8b10209daa4de74427e175ef21ddf306a17a0ae
Signed-off-by: Stamatis Katsaounis <skatsaounis@admin.grnet.gr>

src/lib/charm/openstack/gnocchi.py

@@ -76,6 +76,25 @@ def ceph_config(config):
         return CEPH_CONF
 
 
+class GnocchiCharmDatabaseRelationAdapter(adapters.DatabaseRelationAdapter):
+    """
+    Overrides default class to add binary_prefix option to solve
+    'Invalid utf8 character' warnings
+    """
+
+    def get_uri(self, prefix=None):
+        uri = super(GnocchiCharmDatabaseRelationAdapter, self).get_uri(prefix)
+        release = ch_utils.get_os_codename_install_source(
+            self.config['openstack-origin'])
+        if (ch_utils.OPENSTACK_RELEASES.index(release) >=
+                ch_utils.OPENSTACK_RELEASES.index('rocky')):
+            if '?' in uri:
+                uri += '&binary_prefix=true'
+            else:
+                uri += '?binary_prefix=true'
+        return uri
+
+
 class GnocchiCharmRelationAdapaters(adapters.OpenStackAPIRelationAdapters):
 
     """
@@ -84,7 +103,7 @@ class GnocchiCharmRelationAdapaters(adapters.OpenStackAPIRelationAdapters):
 
     relation_adapters = {
         'storage_ceph': charms_openstack.plugins.CephRelationAdapter,
-        'shared_db': adapters.DatabaseRelationAdapter,
+        'shared_db': GnocchiCharmDatabaseRelationAdapter,
         'cluster': adapters.PeerHARelationAdapter,
         'coordinator_memcached': adapters.MemcacheRelationAdapter,
     }