email: change default from name to Grafana

Changes default from name in smtp settings
from Grafana Admin to Grafana.

Fix for integration test (which is skipped but that
did not work)

docs/sources/http_api/admin.md

@@ -158,7 +158,7 @@ with Grafana admin permission.
         "cert_file":"",
         "enabled":"false",
         "from_address":"admin@grafana.localhost",
-        "from_name":"Grafana Admin",
+        "from_name":"Grafana",
         "host":"localhost:25",
         "key_file":"",
         "password":"************",