added health ready endpoints, fix API base url

[rhajek]

Closes #14

[codecov-io]

Codecov Report

Merging #13 into master will increase coverage by 47.69%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master      #13       +/-   ##
===========================================
+ Coverage    39.5%   87.19%   +47.69%     
===========================================
  Files         300       20      -280     
  Lines       25879     1515    -24364     
===========================================
- Hits        10223     1321     -8902     
+ Misses      15656      194    -15462

Impacted Files	Coverage Δ
influxdb2/client/influxdb_client.py	98.73% <100%> (+5.49%)	⬆️
influxdb2/domain/line_protocol_error.py
influxdb2/domain/node.py
influxdb2/domain/scraper_target_response.py
influxdb2/domain/task_create_request.py
influxdb2/domain/query_variable_properties.py
influxdb2_test/__init__.py
influxdb2/domain/lesser_threshold.py
influxdb2/domain/http_notification_rule.py
influxdb2/domain/decimal_places.py
... and 244 more

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