add jsonpickle and pexpect libs in case of unsafe decoding and secondary command execution, add proper test cases

python/ql/test/library-tests/frameworks/pexpect/ExecCmd.py

@@ -0,0 +1,9 @@
+import pexpect
+from pexpect import popen_spawn
+
+cmd = "ls -la"
+result = pexpect.run(cmd) # $ getCommand=cmd
+result = pexpect.runu(cmd) # $ getCommand=cmd
+result = pexpect.spawn(cmd) # $ getCommand=cmd
+result = pexpect.spawnu(cmd) # $ getCommand=cmd
+result = popen_spawn.PopenSpawn(cmd) # $ getCommand=cmd