scripts/rpc.py: allow users to pipe multiple requests

Users can now pipe a large number of requests to
rpc.py, separated by newlines - each line will be
executed as if it was passed to rpc.py individually.

There is significant savings using this feature when
executing multiple requests through rpc.py.  On my
system, a loop of 30 RPCs related to setting up
10 NVMf subsystems takes 5 seconds when executed
one at a time.  With this new feature, it takes
less than 1 second.

Signed-off-by: Jim Harris <james.r.harris@intel.com>

Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/452770 (master)

(cherry picked from commit 363fe506bc)
Change-Id: Iec957ca67461af8e8c41aee47e1d113714b22d3d
Signed-off-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-on: https://review.gerrithub.io/c/spdk/spdk/+/457220
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>

scripts/rpc.py

@@ -1800,6 +1800,15 @@ Format: 'user:u1 secret:s1 muser:mu1 msecret:ms1,user:u2 secret:s2 muser:mu2 mse
             print(ex.message)
             exit(1)
 
+    def execute_script(parser, client, fd):
+        for rpc_call in map(str.rstrip, fd):
+            args = parser.parse_args(rpc_call.split())
+            args.client = client
+            call_rpc_func(args)
+
     args = parser.parse_args()
     args.client = rpc.client.JSONRPCClient(args.server_addr, args.port, args.timeout, log_level=getattr(logging, args.verbose.upper()))
-    call_rpc_func(args)
+    if hasattr(args, 'func'):
+        call_rpc_func(args)
+    else:
+        execute_script(parser, args.client, sys.stdin)