Opportunistic Encryption program and various related tests added

[Rishabh04-02]

Solves the following issues in Libreswan-Opportunistic-IPsec (GSoC 2019 project):

1. testing: what is behaviour when server restarts cleanly Rishabh04-02/Libreswan-Opportunistic-IPsec#7
2. testing: what happens when server crashes and restarts Rishabh04-02/Libreswan-Opportunistic-IPsec#8
3. testing: the working of two clients behind NAT, with one not using IPsec. Rishabh04-02/Libreswan-Opportunistic-IPsec#13
4. Update conf files location Rishabh04-02/Libreswan-Opportunistic-IPsec#14
5. The 1st ping always goes missing. Rishabh04-02/Libreswan-Opportunistic-IPsec#15
6. ipsec not creating letsencrypt in dir Rishabh04-02/Libreswan-Opportunistic-IPsec#16
7. Testing: what happens when client crashes and restarts. Rishabh04-02/Libreswan-Opportunistic-IPsec#17
8. Testing: what happens when client restarts cleanly. Rishabh04-02/Libreswan-Opportunistic-IPsec#18
9. man ipsec letsencrypt does not work properly Rishabh04-02/Libreswan-Opportunistic-IPsec#19
10. subcommand could use a "-" in name  Rishabh04-02/Libreswan-Opportunistic-IPsec#20
11. long command options for ipsec letsencrypt command Rishabh04-02/Libreswan-Opportunistic-IPsec#21
12. ipsec letsencrypt -client should not start ipsec if ipesc wasn't running at the time Rishabh04-02/Libreswan-Opportunistic-IPsec#22
13. ping test should only run when requested by administrator  Rishabh04-02/Libreswan-Opportunistic-IPsec#23
14. server config should not contain someone elses hostname Rishabh04-02/Libreswan-Opportunistic-IPsec#24
15. add 0.0.0.0/0 to private-or-clear Rishabh04-02/Libreswan-Opportunistic-IPsec#25
16. add: ipsec letsencrypt --disable Rishabh04-02/Libreswan-Opportunistic-IPsec#26

Also, this makes OE possible and make it work with libreswan.

[Rishabh04-02]

Merged https://github.com/libreswan/libreswan/commits?author=Rishabh04-02