tests: avoid side effects of $SHELL environment variable

Since non interactive shells don't generally set $SHELL,
its value is propagated through the tests and may cause issues;
for example if $SHELL implicitly adjusts $PATH when run.
Instead we set $SHELL to that determined by the posix-shell module,
and use that consistently for all test sub scripts,
including those created thorugh the `split --filter` command.

* tests/local.mk: Explicitly set $SHELL to $(PREFERABLY_POSIX_SHELL)
which defaults to $CONFIG_SHELL and thus usually /bin/sh.
* tests/envvar-check: Remove bash environment variables with
side effects, in case /bin/bash was selected for $SHELL.
* tests/misc/help-version.sh: Remove redundant initialization of $SHELL.
* tests/install/strip-program.sh: Use $SHELL for sub script.
* tests/misc/sort-compress-hang.sh: Likewise.
* tests/misc/sort-compress-proc.sh: Likewise.
* tests/misc/sort-compress.sh: Likewise.
* tests/misc/timeout-group.sh: Likewise.
* tests/rm/fail-eperm.xpl: Remove redundant elision of bash env vars.
* tests/misc/pwd-long.sh: Likewise.

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/install/strip-program.sh b/tests/install/strip-program.sh
index 7ac2165ea..103f54943 100755
--- a/tests/install/strip-program.sh
+++ b/tests/install/strip-program.sh
@@ -22,7 +22,7 @@ print_ver_ ginstall
 working_umask_or_skip_
 
 cat <<EOF > b || framework_failure_
-#!$PREFERABLY_POSIX_SHELL
+#!$SHELL
 sed s/b/B/ \$1 > \$1.t && mv \$1.t \$1
 EOF
 chmod a+x b || framework_failure_