Fix os resource script (bugfix)

[pieqq]

Description

Replace get_release_file_path function with get_release_file_content
that tries to access /var/lib/snapd/hostfs/etc/os-release. If this
file doesn't exist, it means we are not calling the script from within a
snap, so it tries to access /etc/os-release instead.

get_release_info now takes the content of the os-release file as
parameter and ignores empty lines.

The issue was introduced with previous PR #1748

Resolved issues

Prevent the os resource job from failing like this (example found the submission from a run using Checkbox in the edge channel):

{
            "id": "lsb",
            "full_id": "com.canonical.certification::lsb",
            "name": "[DEPRECATED, use 'os' instead] Collect information about installed operating system (os-release)",
            "certification_status": "non-blocker",
            "category": "Gathers information about the DUT",
            "category_id": "com.canonical.certification::information_gathering",
            "status": "fail",
            "outcome": "fail",
            "comments": null,
            "io_log": "Traceback (most recent call last):\n  File \"/tmp/nest-kopwzdp5.810b3c2c743e7de21a0c69775e0ca9675ca511eed3b76c394124412985b763db/os_resource.py\", line 57, in <module>\n    sys.exit(main())\n  File \"/tmp/nest-kopwzdp5.810b3c2c743e7de21a0c69775e0ca9675ca511eed3b76c394124412985b763db/os_resource.py\", line 51, in main\n    release_info = get_release_info(release_file_path)\n  File \"/tmp/nest-kopwzdp5.810b3c2c743e7de21a0c69775e0ca9675ca511eed3b76c394124412985b763db/os_resource.py\", line 39, in get_release_info\n    with open(release_file_path, \"r\") as lsb:\nFileNotFoundError: [Errno 2] No such file or directory: '/var/lib/snapd/hostfs/etc/os-release'\n",
            "type": "test",
            "project": "certification",
            "duration": 0.15081572532653809,
            "plugin": "resource",
            "template_id": null
        },

Documentation

Tests

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 2 lines in your changes missing coverage. Please review.

Project coverage is 49.82%. Comparing base (b6fe2e7) to head (874932d).
Report is 118 commits behind head on main.

Files with missing lines	Patch %	Lines
providers/resource/bin/os_resource.py	83.33%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1786   +/-   ##
=======================================
  Coverage   49.81%   49.82%           
=======================================
  Files         377      377           
  Lines       40701    40703    +2     
  Branches     6844     6846    +2     
=======================================
+ Hits        20277    20279    +2     
  Misses      19700    19700           
  Partials      724      724           

Flag	Coverage Δ
provider-resource	∅ <85.71%> (∅)

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