Merge branch 'https-coverage-v6'

This patchset adds some basic tests to cover some https cases:
$ regress +http/https_..
http/https_basic: [forking] OK
http/https_simple: [forking] OK
http/https_simple_dirty: [forking] OK
http/https_incomplete: [forking] OK
http/https_incomplete_timeout: [forking] OK
http/https_connection_retry: [forking] OK
http/https_connection_retry_conn_address: [forking] OK
7 tests ok.  (0 skipped)

But there are some leaks in http regression tests (like init_ssl() and others),
must be fixed by using custom setup routine.

* https-coverage-v6:
  test/http: allow dirty shutdown for ssl to fix https_incomplete
  test/http: https basic
  test/http: incomplete{,_timeout} for https
  test/http: add simplest test for http/https/https_dirty_shutdown
  test/http: https: retry coverage
  test/http: https server support (plus some helpers)
  test/http: more sanity checks
  test/ssl: export getkey()/getcert()/get_ssl_ctx()/init_ssl() for https