plugins/python/regress: add a testcase for multiple io plugin loading

to verify 2 python plugins can work next to each other.

plugins/python/regress/testdata/check_example_io_plugin_command_log_multiple.stdout

@@ -0,0 +1,2 @@
+Example sudo python plugin will log to /tmp/sudo_check_python_exampleXXXXXX/sudo.log
+Example sudo python plugin will log to /tmp/sudo_check_python_exampleXXXXXX2/sudo.log

plugins/python/regress/testdata/check_example_io_plugin_command_log_multiple1.stored

@@ -0,0 +1,16 @@
+ -- Plugin STARTED --
+EXEC id --help
+EXEC info [
+    "command=/bin/id",
+    "runas_uid=0"
+]
+STD IN stdin for plugin 1
+STD OUT stdout for plugin 1
+STD ERR stderr for plugin 1
+SUSPEND SIGTSTP
+SUSPEND SIGCONT
+WINSIZE 20x10
+TTY IN tty input for plugin 1
+TTY OUT tty output for plugin 1
+CLOSE Command returned 1
+ -- Plugin DESTROYED --

plugins/python/regress/testdata/check_example_io_plugin_command_log_multiple2.stored

@@ -0,0 +1,16 @@
+ -- Plugin STARTED --
+EXEC whoami
+EXEC info [
+    "command=/bin/whoami",
+    "runas_uid=1"
+]
+STD IN stdin for plugin 2
+STD OUT stdout for plugin 2
+STD ERR stderr for plugin 2
+SUSPEND SIGSTOP
+SUSPEND SIGCONT
+WINSIZE 30x40
+TTY IN tty input for plugin 2
+TTY OUT tty output for plugin 2
+CLOSE Command returned 2
+ -- Plugin DESTROYED --