cleanup boltdb files in queriers during startup/shutdown

[sandeepsukhani]

What this PR does / why we need it:
Queriers do not use existing boltdb files when they receive a query for a new table(never served queries for it since startup) and we do not remove boltdb files when queriers stop which means unwanted files would be lying around.

This PR removes files from the cache directory during graceful shutdown or during startup if it didn't get to remove them for some reason.

Ideally, it would be good to reuse those files but the files could be stale and we would have to sync them first with the store which would add up to startup delay. We can handle this in future incremental changes.

[codecov-commenter]

Codecov Report

Merging #2558 into master will increase coverage by 0.03%.
The diff coverage is 12.50%.

@@            Coverage Diff             @@
##           master    #2558      +/-   ##
==========================================
+ Coverage   62.98%   63.01%   +0.03%     
==========================================
  Files         168      168              
  Lines       14879    14886       +7     
==========================================
+ Hits         9371     9380       +9     
  Misses       4762     4762              
+ Partials      746      744       -2     

Impacted Files	Coverage Δ
.../storage/stores/shipper/downloads/table_manager.go	67.74% <0.00%> (-3.05%)	⬇️
pkg/storage/stores/shipper/downloads/table.go	68.12% <25.00%> (-0.47%)	⬇️
pkg/querier/queryrange/downstreamer.go	95.87% <0.00%> (-2.07%)	⬇️
pkg/logql/evaluator.go	92.88% <0.00%> (+0.40%)	⬆️
pkg/promtail/targets/file/filetarget.go	69.14% <0.00%> (+2.28%)	⬆️
pkg/promtail/targets/file/tailer.go	75.00% <0.00%> (+4.16%)	⬆️

[slim-bean]

LGTM!