pam/main-exec: Exit with failure if the the server connection is lost

[3v1n0]

In case the DBus connection that the module provides has gone away we should also stop the client, so that there won't be a dangling process around.

This happens for example when a login timeout occurs, as in such case the PAM module connection goes away, while it's child is not.

Add tests checking this is the case.

This is enough to solve #903, while we can also use more low-level stuff, but for sure we've to die if the connection is lost, for whatever reason.

UDENG-6770

[codecov-commenter]

Codecov Report

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

Project coverage is 85.53%. Comparing base (c27fba1) to head (8b07100). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pam/internal/dbusmodule/transaction.go	50.00%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #904      +/-   ##
==========================================
+ Coverage   85.52%   85.53%   +0.01%     
==========================================
  Files          82       82              
  Lines        5707     5712       +5     
  Branches      109      109              
==========================================
+ Hits         4881     4886       +5     
  Misses        771      771              
  Partials       55       55              

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[adombeck]

@3v1n0 what was the status here? I seem to remember that this branch had some issue and we decided that we want to go ahead with https://github.com/ubuntu/authd/pull/903 instead, but I'm not sure.

[3v1n0]

Maybe only with the part of #903 doing the killing, although I'm still curious to understand why this fail, that could be an issue we could just hide otherwise :thinking: