refactor tests to reduce duplication
Rename server.conf.erb to server-default.conf.erb and create _default partial templates

Split out server template into two parts:
server/_default-{header,footer}.conf.erb which hold unchaning values
server-default.conf.erb which contains commonly modified values, and
imports _default.conf.erb
Change default template to server-default.conf.erb
Update tests to check content of server.conf
Add server-hostname template and tests
Update documentation to explain default behaviour of rsyslog::server and suggest alternative