Returncode fix (#1)

Some trial and error to make sure it works reliably.

* remove test_retcode
* debug local bash settings
* set errexit explicitly in subshell
* set errexit also in the subshell in parenthesis
* debugging
* more debugging (exit code of sh)
* is the venv subshell returning exit 1?
* what if we remove the additional subshell?
* then we need to unquote the command
* if statement needs test command quoted
* simple if statement
* echo command needs to be removed of course
* remove debug statements
* check if setting errexit here is needed
* these settings can be removed
  At this point ("before") the shell already has errexit set.
* setting errexit in the sh invocation is needed
  This is not inherited, so it's good to specify it.
* just double checking that the subshell doesn't exit
* use solution from fvue.nl
* Solution doesn't seem to work, even popd is run
  So now I'm putting back the if statement, it seems
  to be the simplest and most effective solution.
* add a comment
* prove that errexit is necessary
* errexit is indeed needed for chaining

cibuildwheel/linux.py

@@ -57,8 +57,6 @@ def build(project_dir, output_dir, test_command, test_requires, test_extras, bef
             mkdir /output
             cd /project
 
-            test_retcode=0
-
             {environment_exports}
 
             for PYBIN in {pybin_paths}; do
@@ -111,10 +109,13 @@ def build(project_dir, output_dir, test_command, test_requires, test_extras, bef
 
                         # Run the tests from a different directory
                         pushd $HOME
-                        sh -c {test_command}
+                        sh -o errexit -c {test_command}
                         popd
                     )
-                    test_retcode=$(( $test_retcode || $? ))
+                    # exit if tests failed
+                    if [ $? -ne 0 ]; then
+                      exit 1;
+                    fi
 
                     # clean up
                     rm -rf "$venv_dir"
@@ -124,8 +125,6 @@ def build(project_dir, output_dir, test_command, test_requires, test_extras, bef
                 mv "$delocated_wheel" /output
                 chown {uid}:{gid} "/output/$(basename "$delocated_wheel")"
             done
-
-            exit $test_retcode
         '''.format(
             pybin_paths=' '.join(c.path+'/bin' for c in platform_configs),
             test_requires=' '.join(test_requires),