bitbake: asyncrpc: Add context manager API

Adds context manager API for the asyncrcp client class which allow
writing code that will automatically close the connection like so:

    with hashserv.create_client(address) as client:
       ...

Rework the bitbake-hashclient tool and PR server to use this new API to
fix warnings about unclosed event loops when exiting

(Bitbake rev: 52226a7244968c8dad6f4ee9ccec57ac1979217a)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit d01d684a0f6398270fe35ed59b7d28f3fd9b7e41)
Signed-off-by: Steve Sakoman <steve@sakoman.com>

bitbake/lib/prserv/serv.py

@@ -344,9 +344,9 @@ def auto_shutdown():
 def ping(host, port):
     from . import client
 
-    conn = client.PRClient()
-    conn.connect_tcp(host, port)
-    return conn.ping()
+    with client.PRClient() as conn:
+        conn.connect_tcp(host, port)
+        return conn.ping()
 
 def connect(host, port):
     from . import client