Refactor generate_queries devops case to use errs

[RobAtticus]

Previously the devops use case generation code used a call to
log.Fatalf when something went wrong. This makes it awkward to test
error conditions when generating queries from other packages, since
we need a way to (a) replace the unexported call to log.Fatalf and
(b) prevent the runtime from actually quitting.

It is better for the library to actually return errors on calls
that can fail, rather than either fataling or panicking. Now other
packages can handle the errors themselves and also test error
conditions in their packages as well.

This refactor was pruned a bit to bubble the 'panic' up one level
for now. When the actual generation code encounters the error
during normal execution, it will panic. But these are easier to
test for and don't require adding hooks to replace the 'fatal'
path in the original package.

[codecov-io]

Codecov Report

Merging #77 into master will decrease coverage by 0.31%.
The diff coverage is 49.49%.

@@            Coverage Diff             @@
##           master      #77      +/-   ##
==========================================
- Coverage   57.13%   56.82%   -0.32%     
==========================================
  Files          76       76              
  Lines        3719     3757      +38     
==========================================
+ Hits         2125     2135      +10     
- Misses       1570     1592      +22     
- Partials       24       30       +6

Impacted Files	Coverage Δ
...bs_generate_queries/databases/clickhouse/devops.go	10.1% <20%> (+0.16%)	⬆️
...sbs_generate_queries/databases/cassandra/devops.go	25.55% <28.57%> (+0.86%)	⬆️
...d/tsbs_generate_queries/databases/influx/devops.go	32.14% <28.57%> (+0.14%)	⬆️
...d/tsbs_generate_queries/databases/siridb/devops.go	27.58% <28.57%> (+0.66%)	⬆️
...s_generate_queries/databases/timescaledb/devops.go	97.41% <87.5%> (-1.2%)	⬇️
cmd/tsbs_generate_queries/uses/devops/common.go	92.85% <90.47%> (-3.97%)	⬇️

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[antekresic]

I must admit, I did find this ironic when I first read it 😄

[RobAtticus]

yeah enjoyed a nice chuckle as I removed it

[antekresic]

Thanks for this!

I wanted to do it myself but decided to finish up the current PR that I had in line before doing that.