software/grafana: promise to check influxdb is usable

This should fix this random failure with tests:

    ======================================================================
    FAIL: test_influxdb_api (test.TestInfluxDb)
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "parts/slapos-repository/software/grafana/test/test.py", line 126, in test_influxdb_api
        [connection_params['influxdb-database']], result['series'][0]['values'])
    AssertionError: ['telegraf'] not found in [[u'_internal']]

software/grafana/buildout.hash.cfg

@@ -15,7 +15,7 @@
 
 [instance-profile]
 filename = instance.cfg.in
-md5sum = 214a756a6a9f73455411760b2daa25b7
+md5sum = 0edf9e67bc637d73a7415124c8082a8c
 
 [influxdb-config-file]
 filename = influxdb-config-file.cfg.in

software/grafana/instance.cfg.in

@@ -126,6 +126,18 @@ command-line =
   {{ influx_bin }} -username ${influxdb:auth-username} -password ${influxdb:auth-password} -socket ${influxdb:unix-socket} -execute "CREATE USER ${influxdb:auth-username} WITH PASSWORD '${influxdb:auth-password}' WITH ALL PRIVILEGES"
 wrapper-path = ${directory:promise}/${:_buildout_section_name_}
 
+[influxdb-database-ready-promise]
+recipe = slapos.cookbook:wrapper
+command-line =
+  bash -c "{{ influx_bin }} \
+     -username ${influxdb:auth-username} \
+     -password ${influxdb:auth-password} \
+     -host ${influxdb:host} \
+     -port ${influxdb:http-port} \
+     -unsafeSsl \
+     -ssl \
+     -execute 'show databases' | grep '${influxdb:database}'"
+wrapper-path = ${directory:promise}/${:_buildout_section_name_}
 
 
 [grafana]
@@ -261,6 +273,7 @@ recipe =
 instance-promises =
   ${influxdb-listen-promise:path}
   ${influxdb-password-promise:wrapper-path}
+  ${influxdb-database-ready-promise:wrapper-path}
   ${grafana-listen-promise:path}
   ${loki-listen-promise:path}
   ${promtail-listen-promise:path}