This commit adds mount output to the error raised by
FileSystemMountService.mount(). This is useful when running into
mount failures during osbuild runs.
The issue was discovered while debugging a mount failure for
osbuild-composer PR#3820. Initially osbuild PR#1490 was meant
to fix it but it turned out there is a third mount helper in
the code that was originally overlooked (sorry for that!).
While debugging a failure of osbuild-composer [0] on fc39 it was
noticed that a mount failure does not include the output of
the mount command:
```
File "/usr/lib/python3.12/site-packages/osbuild/mounts.py", line 78, in mount
path = client.call("mount", args)
^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/site-packages/osbuild/host.py", line 348, in call
ret, _ = self.call_with_fds(method, args)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/site-packages/osbuild/host.py", line 384, in call_with_fds
raise error
osbuild.host.RemoteError: CalledProcessError: Command '['mount', '-t', 'xfs', '-o', 'ro,norecovery', '--source', '/dev/rootvg/applv', '--target', '/tmp/tmpjtfmth56/app']' returned non-zero exit status 32.
File "/usr/lib/python3.12/site-packages/osbuild/host.py", line 268, in serve
reply, reply_fds = self._handle_message(msg, fds)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/site-packages/osbuild/host.py", line 301, in _handle_message
ret, fds = self.dispatch(name, args, fds)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/site-packages/osbuild/mounts.py", line 111, in dispatch
r = self.mount(args)
^^^^^^^^^^^^^^^^
File "/usr/lib/python3.12/site-packages/osbuild/mounts.py", line 160, in mount
subprocess.run(
File "/usr/lib64/python3.12/subprocess.py", line 571, in run
raise CalledProcessError(retcode, process.args,
```
which makes diagnostic errors harder of course. This commit adds
a test that ensures that mount output is visbile and also changes
the code to include it.
[0] https://github.com/osbuild/osbuild-composer/pull/3820
