h2load has supported uploading a file quite a while, but it turns out
that it worked with HTTP/2 and SPDY only.  HTTP/1 with upload did not
work.  This commit fixes this bug, and implement HTTP/1 upload.  Due
to architectural limitation of h2load, when -d option is used, the
number of in-flight pipe-lined requests is set to 1.

Suppose the wildcard patterns follows:

- *.nghttp2.org/foo
- *.img.nghttp2.org/bar

Previously, s.img.nghttp2.org/foo does not match anything.  Now it
matches first pattern.

Instead of using bool flag, just stop prepare watcher.

This is a legacy of SPDY era where it can disable flow control.