fix HAS_HOST and HAS_NSLOOKUP condition

Check for domain using all tools

Remove dependency on seq, ensure clean_up doesn't try to delete /tmp

Improvements: alternative working dirs and -i|--install command

Clean code, avoid indirect variables and single quotes for delayed expansion.

While testing or setting up getssl the installation of certificates
could fail. Option -i allows to copy and reload service quicker.

Despite changing working dir from command line covers most usage cases,
others defaults are also usefull like /etc/getssl, SCRIPTDIR/conf or
SCRIPTDIR/.getssl. Last candidate (~/.getssl) is used if no config file
was found in previous paths.

Fixed for mixed case domain names

Fix domain template url (failing tests are a git checkout issue)

Pre-release 2.21

The trailing slash of the Let's Encrypt staging server URL broke API discovery

Test on centos7 against staging server

Parallelize the gitactions tests