Fix hardening measure in release extraction

[grembo]

In #49 a hardening measure was imported from truenas/iocage#358. This hardening measure limits what can be extracted (location and attributes). It is implemented by applying the 'tar' filter from tarfile. That filter does this[0]:

• Strip leading slashes (/ and os.sep) from filenames.
• Refuse to extract files with absolute paths (in case the name is absolute even after stripping slashes, e.g. C:/foo on Windows). This raises AbsolutePathError.
• Refuse to extract files whose absolute path (after following symlinks) would end up outside the destination. This raises OutsideDestinationError.
• Clear high mode bits (setuid, setgid, sticky) and group/other write bits (S_IWGRP | S_IWOTH).

While the first three modifications are desirable, the last one damages the extracted release image, as things like sticky bits and world writable files are required by a proper FreeBSD (jail) installation.

Fixes #54

[0]https://docs.python.org/3/library/tarfile.html#tarfile-extraction-filter

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[coveralls]

Pull Request Test Coverage Report for Build 12223403055

Details

• 0 of 15 (0.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 7.733%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
iocage_lib/ioc_fetch.py	0	15	0.0%

Files with Coverage Reduction	New Missed Lines	%
iocage_lib/release.py	1	0.0%

Totals
Change from base Build 12088701378:	-0.02%
Covered Lines:	799
Relevant Lines:	7815

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💛 - Coveralls