REGTESTS: server: fix agent-check syntax and expectation

Since commit 8d6c6bd ("Leak-plugging on barriers") VTest has become
stricter in its expectations, making this one fail. The agent-check
test was expecting a close on the server, which normally does not
happen before the server responds. In addition, it was really sending
"hello" (with the quotes) due to the config file syntax, which explains
why test test log reported that '"hell' was received, and complained
that 0x6f ('o') was read instead of a shutdown. This has been fixed
as well by using single-quotes.

There is no need to backport this test as it's only in 2.5.
diff --git a/reg-tests/server/cli_add_check_server.vtc b/reg-tests/server/cli_add_check_server.vtc
index 576ef3c..31d4d61 100644
--- a/reg-tests/server/cli_add_check_server.vtc
+++ b/reg-tests/server/cli_add_check_server.vtc
@@ -19,7 +19,6 @@
 server s3 {
 	recv 5
 	send "ready up\n"
-	expect_close
 	barrier b2 sync
 } -start
 
@@ -103,7 +102,7 @@
 
 # agent check
 haproxy h1 -cli {
-	send "experimental-mode on; add server be1/s3 ${s1_addr}:${s1_port} agent-check agent-addr ${s3_addr} agent-port ${s3_port} agent-send \"hello\" agent-inter 200ms rise 1 fall 1"
+	send "experimental-mode on; add server be1/s3 ${s1_addr}:${s1_port} agent-check agent-addr ${s3_addr} agent-port ${s3_port} agent-send 'hello' agent-inter 200ms rise 1 fall 1"
 	expect ~ "New server registered."
 
 	send "enable agent be1/s3"