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

Prefer dig on config check over nslookup and drill with ubuntu