Show puppetdb connection error message on homepage

[ArthurWuTW]

• Able to show error message on homepage when puppetdb connection failed.
  

• Able to show 0 nodes on homepage without any agents yet.
  

[codecov]

Codecov Report

Merging #692 (71afad4) into master (1c5a719) will decrease coverage by 0.36%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master     #692      +/-   ##
==========================================
- Coverage   86.29%   85.93%   -0.37%     
==========================================
  Files          19       19              
  Lines        1051     1059       +8     
==========================================
+ Hits          907      910       +3     
- Misses        144      149       +5     

Impacted Files	Coverage Δ
puppetboard/views/query.py	86.04% <50.00%> (-2.05%)	⬇️
puppetboard/app.py	91.48% <100.00%> (+0.18%)	⬆️
puppetboard/views/index.py	95.00% <100.00%> (+0.08%)	⬆️
puppetboard/views/failures.py	26.19% <0.00%> (-2.76%)	⬇️
puppetboard/views/reports.py	64.96% <0.00%> (+0.25%)	⬆️

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[gdubicki]

This implementation is definitely an improvement, but if you would use the error handlers feature from Flask then it would work on any view, not just the Overview. Have you thought of that, @ArthurWuTW?

[ArthurWuTW]

At first I wanted to make the minimal change to achieve those improvements for Overview only, but the error handler feature looks nice, I will check it out and give it a try :)

I'm new to codecov, what is the check of "codecov/project" for? it failed but I'm not really sure what the problem is...

[ArthurWuTW]

I just found that it has already had error handlers in code base.
Just import errors.py and skip env_check when env=default_env(to show 0 nodes).

• start puppetboard only - error message is clear enough
  

• start puppetboard and puppetdb with 0 nodes
  
  

• start puppetboard and puppetdb with 1 node
  

[gdubicki]

I just found that it has already had error handlers in code base.

Oups, I have really forgotten about it...

Well, anyway, it's great that we can achieve what we want with the minimal amount of changes that we have in this PR.

Can you also just please test if the Query view still behaves like it did? It's the only screen where we expect to return 400 or 404 in a normal day-to-day use, when a user enters an invalid query or it returns zero results. Please see #653 for a reference, if needed.

If we still show the user-friendly messages there then I think we can merge and release this.

[ArthurWuTW]

before this commit 71afad4, when 0 nodes, Query was like...

if we need to be able to query when 0 nodes, we need to add the same condition to skip env_check as Overview, and Query behaves as normal.

[gdubicki]

Thanks @ArthurWuTW, I think we are good to go with this now. :)