[lit] Fix order of checks in shtest-shell.py test

[modocache]

Summary

An expectation in utils/lit/tests/Inputs/shtest-shell/redirects.txt
expects that first a string printed to stdout is seen, and then a
string printed to stderr. Add flush() calls to ensure that stdout is
printed before stderr, as expected.

[modocache]

Update commit message

[rnk]

lgtm

[modocache]

Thanks!

utils/lit/tests/Inputs/shtest-shell/write-to-stderr.py

 #!/usr/bin/env python
+
 import sys
+
+
 sys.stderr.write("a line on stderr\n")
+sys.stderr.flush()

utils/lit/tests/Inputs/shtest-shell/write-to-stdout-and-stderr.py

 #!/usr/bin/env python
+
 import sys
+
+
 sys.stdout.write("a line on stdout\n")
+sys.stdout.flush()
+
 sys.stderr.write("a line on stderr\n")
+sys.stderr.flush()