Remove "which" declaration from env vars in EL8+ tests

EL8+ systems declare "which" function using environment variables in the
/etc/profile.d/which2.sh file. Because of our suboptimal environment
variable detection, which is required in order to support the legacy
runner, these variables are picked up by the pytest runner.

If subprocesses are spawned with these environment variables set, it
will cause the following issue when they spawn yet another subprocess:

/bin/sh: which: line 1: syntax error: unexpected end of file
/bin/sh: error importing function definition for `which'

(cherry picked from commit 68b1c6877b)

bin/tests/system/conftest.py

@@ -143,6 +143,10 @@ else:
         for line in env_bytes.splitlines():
             match = ENV_RE.match(line)
             if match:
+                # EL8+ workaround for https://access.redhat.com/solutions/6994985
+                # FUTURE: can be removed when we no longer need to parse env vars
+                if match.groups()[0] in [b"which_declare", b"BASH_FUNC_which%%"]:
+                    continue
                 out[match.groups()[0]] = match.groups()[1]
         return out