Use RTLD_NODELETE=true when loading libraries

[azeey]

Fixes (Potentially): #806

Summary

Gazebo Garden crashes at exit because the destructor for an EventT object created by a gui plugin is accesses after the plugin is unloaded. For that particular crash, the plugin in question is in gz-gui, so I've submitted a fix there (gazebosim/gz-gui#469). This PR is proactively using RTLD_NODELETE to prevent future bugs of this nature.

I believe this might also fix #806 because if the shared libraries never get deleted, when a plugin goes through a load--unload--load cycle, the components (more specifically, the vtable of the components) it registers will be located in the same memory address. This was not the case before, which I think was the culprit for many of the flakiness in macOS.

More context:

• Fix segfault when destroying Event objects gz-common#367

Requires:

• Add option to use RTLD_NODELETE when loading a library gz-plugin#102

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[chapulina]

@osrf-jenkins run tests please

[chapulina]

This test is failing on all platforms 😕

[chapulina]

Actually, this is using nightlies of plugin2, but not of gui7 yet, let me trigger some:

• 
• 

[chapulina]

Ok, now it passes on Ubuntu, but it's failing on macOS:

61: [ RUN      ] WorldFiles/GazeboDeathTest.CleanExit/0
61: 
61: [WARNING] /Users/jenkins/workspace/ignition_gazebo-ci-pr_any-homebrew-amd64/ign-gazebo/test/gtest_vendor/src/gtest-death-test.cc:1108:: Death tests use fork(), which is unsafe particularly in a threaded context. For this test, Google Test detected 3 threads. See https://github.com/google/googletest/blob/master/docs/advanced.md#death-tests-and-threads for more explanation and suggested solutions, especially if this is the last message you see before your test times out.
61: /Users/jenkins/workspace/ignition_gazebo-ci-pr_any-homebrew-amd64/ign-gazebo/src/gui/Gui_clean_exit_TEST.cc:97: Failure
61: Death test: startBoth(sdfFile)
61:     Result: died but not with expected exit code:
61:             Terminated by signal 11
61: Actual msg:
61: [  DEATH   ] The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec().
61: [  DEATH   ] Break on __THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__() to debug.
61: [  DEATH   ] 
61: [  FAILED  ] WorldFiles/GazeboDeathTest.CleanExit/0, where GetParam() = "empty.sdf" (50 ms)

Windows is also failing, but it doesn't even find the shared libraries.

I'm going to disable the test for macOS and Windows.

[azeey]

Also only enabled on Linux in Fortress, so thanks for making the change in f0c2c27

[codecov]

Codecov Report

Merging #1649 (5118037) into gz-sim7 (0942c2e) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 5118037 differs from pull request most recent head f0c2c27. Consider uploading reports for the commit f0c2c27 to get more accurate results

@@           Coverage Diff            @@
##           gz-sim7    #1649   +/-   ##
========================================
  Coverage    63.90%   63.90%           
========================================
  Files          334      334           
  Lines        26344    26344           
========================================
  Hits         16836    16836           
  Misses        9508     9508           

Impacted Files	Coverage Δ
src/SystemLoader.cc	54.54% <100.00%> (ø)

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