ARROW-4179: [Python] Use more public API to determine whether a test has a pytest mark or not

[wesm]

There was an internal API change in pytest 4.1.0 that resulted in our pytest configuration logic failing to check if marks were set or not on unit tests. I confirmed that the following fixes the problem both on pytest 4.0.x (where things still worked) and 4.1.0 (when things broke)

[kszucs]

Triggered crossbow conda and wheel tests too (don't need to wait though).

[codecov-io]

Codecov Report

Merging #3333 into master will decrease coverage by 19.28%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##           master    #3333       +/-   ##
===========================================
- Coverage   87.71%   68.43%   -19.29%     
===========================================
  Files         449      373       -76     
  Lines       53077    48578     -4499     
===========================================
- Hits        46557    33243    -13314     
- Misses       6411    15335     +8924     
+ Partials      109        0      -109

Impacted Files	Coverage Δ
python/pyarrow/tests/conftest.py	74.19% <66.66%> (ø)
cpp/src/arrow/util/memory.h	0% <0%> (-100%)	⬇️
cpp/src/parquet/hasher.h	0% <0%> (-100%)	⬇️
cpp/src/gandiva/to_date_holder.h	0% <0%> (-100%)	⬇️
cpp/src/arrow/io/hdfs-internal.h	0% <0%> (-100%)	⬇️
cpp/src/arrow/util/sse-util.h	0% <0%> (-100%)	⬇️
cpp/src/arrow/pretty_print.h	0% <0%> (-100%)	⬇️
cpp/src/parquet/murmur3.h	0% <0%> (-100%)	⬇️
cpp/src/arrow/util/int-util.cc	0.39% <0%> (-99.21%)	⬇️
cpp/src/arrow/ipc/json-simple.cc	0.41% <0%> (-98.76%)	⬇️
... and 444 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ed1d60d...646c1cb. Read the comment docs.