Support addressing_style for rohmu s3 configurations

[bugant]

Support addressing_style for rohmu s3 configurations: this can be useful to support S3-compatible object storage that requires to use the (deprecated?) path style addressing.

[codecov-commenter]

Codecov Report

Merging #146 (066a3d3) into master (7477bfd) will increase coverage by 0.79%.
Report is 159 commits behind head on master.
The diff coverage is 85.88%.

@@            Coverage Diff             @@
##           master     #146      +/-   ##
==========================================
+ Coverage   87.02%   87.82%   +0.79%     
==========================================
  Files         122      136      +14     
  Lines        7648     9163    +1515     
==========================================
+ Hits         6656     8047    +1391     
- Misses        992     1116     +124     

Files	Coverage Δ
astacus/common/asyncstorage.py	100.00% <100.00%> (ø)
astacus/common/cachingjsonstorage.py	96.49% <100.00%> (+0.06%)	⬆️
astacus/common/cassandra/client.py	92.85% <100.00%> (ø)
astacus/common/cassandra/config.py	75.75% <100.00%> (-11.75%)	⬇️
astacus/common/cassandra/utils.py	100.00% <100.00%> (ø)
astacus/common/etcd.py	94.11% <100.00%> (+0.11%)	⬆️
astacus/common/ipc.py	100.00% <100.00%> (ø)
astacus/common/limiter.py	100.00% <100.00%> (ø)
astacus/common/magic.py	100.00% <100.00%> (ø)
astacus/common/op.py	96.42% <100.00%> (ø)
... and 93 more

... and 2 files with indirect coverage changes

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[bugant]

This is not strictly needed at the moment, so we can probably think of resolving this by including models from rohmu directly? If needed, will re-open it.