fix permissions of files created with dump_to_path

[OriHoch]

Reproduction Steps

• Create a file using standard Python: open("test.txt", "w").write("Hello World!")
• Run a flow with dump_to_path: DF.Flow(({'a': 1},{'a': 2}), DF.dump_to_path('test')).process()

Expected

• Default OS file permissions (from umask):

$ ls -l test.txt
-rw-rw-r-- 1 ori ori 12 Aug 23 19:03 test.txt
$ ls -l test/
-rw-rw-r-- 1 ori ori 816 Aug 23 19:03 datapackage.json
-rw-rw-r-- 1 ori ori   9 Aug 23 19:03 res_1.csv

Actual

• dump_to_path files have permissions to owner only:

$ ls -l test/
-rw------- 1 ori ori 816 Aug 23 19:06 datapackage.json
-rw------- 1 ori ori   9 Aug 23 19:06 res_1.csv

Explanation

Files created with FileDumper are first created as temporary files which have permissions only for file owner, and are are later copied over to the final location. They are copied with the limited temporary file permissions which is unexpected and limited. This PR fixes it by setting their permissions to the default OS permissions as set by umask.

See more details about this problem and the solution here: https://stackoverflow.com/questions/7150826/how-can-i-get-the-default-file-permissions-in-python

[coveralls]

Pull Request Test Coverage Report for Build 552

• 8 of 8 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 84.895%

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Totals
Change from base Build 551:	0.04%
Covered Lines:	2175
Relevant Lines:	2562

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💛 - Coveralls

[akariv]

This is awesome @OriHoch , thanks!
I've bumped my head on this problem some time ago but didn't get to any conclusion.