nghttpx: Fix connection preface is not read by upstream_http2_connhd_readcb

It seems that if readcb is not set before SSL/TLS handshake, the
incoming data already available when eventcb (BEV_EVENT_CONNECTED
event) is fired is not further notified after setting new readcb.  We
knew this fact and call upstream->on_read() in eventcb, but it is
wrong for HTTP/2.  We have to call upstream_http2_connhd_readcb to
check connection preface.  Otherwise, we consume it by nghttp2 session
and it is treated as unknown frame and connection preface is not
detected properly.
h2load: Call session->on_write() explicitly in Client::on_connect()
nghttpx: Remove per-connection rate limit

It looks like setting read-rate and read-burst to 0 makes busy loop.
It seems a bug.  On the other hand, we most likely want per-thread
rate limit rather than per-connection.  So we decided to drop them.
nghttpx: Remove TLSv1.0 from default TLS proto list
nghttpx: Update cipher suite list
nghttp: Remove garbage for deprecated per-stream compression which cause leak
h2load: Fix memory leak detected by LeakSanitizer
Allocate header table ringbuffer lazily

Previously in inflater we reserve new ringbuffer when table size is
changed.  This may be potentially a problem if new table size is very
large number.  When inflater is not used directly by application, this
is not a problem because application can choose the buffer size.  On
the other hand, if application uses inflater directly and it does not
have control of new buffer size (e.g., protocol dissector), then we
just fail to allocate large buffer in
nghttp2_hd_inflate_change_table_size() without actually use such huge
buffer.  This change defers the actual allocation of buffer when it is
actually needed so that we will fail when it is absolutely needed.
h2load: Set number of request per client explicitly

Previously we do not specify the number of requests each client has to
issue.  The each client corresponds to 1 TCP connection.  If
connection was not accepted by server or not TLS handshake is not
done, we effectively don't use that connection and the requests
supposed to be issued for those connections are done via other
established connections.  If this occurs, servers which do not accept
all connections may gain good benchmark results since they don't have
to pay extra cost to handle all connections (e.g., SSL/TLS handshake).
This change explicitly set the number of requests each client has to
issue so that servers cannot *cheat*.
Remove BLOCKED frame