Expect for another variant of error message when gdbserver cannot resolve hostname

I've noticed that on a few hosts, when given an invalid hostname,
gdbserver fails with:

  spawn /../../gdb/gdbserver/gdbserver --once tcp8:123:2353 /gdb/build/fedora-s390x/build/gdb/testsuite/outputs/gdb.server/server-connect/server-connect
  tcp8:123:2353: cannot resolve name: No address associated with hostname
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  Exiting

Unfortunately, this causes a fail on the new
gdb.server/server-connect.exp test (introduced by the IPv6 patch):

  FAIL: gdb.server/server-connect.exp: tcp8: start gdbserver: gdbserver should fail but did not

This happens because we're expecting for another variant of this error
message:

  cannot resolve name: Name or service not known

Therefore, this patch extends the helper function 'gdbserver_start' to
also recognize the "No address associated with hostname" message.
This "fixes" the testcase on the hosts that use this variant.

gdb/testsuite/ChangeLog:
2018-07-13  Sergio Durigan Junior  <sergiodj@redhat.com>

	* lib/gdbserver-support.exp (gdbserver_start): Expect for the
	message "No address associated with hostname" when gdbserver
	cannot resolve the hostname.

gdb/testsuite/ChangeLog

@@ -1,3 +1,9 @@
+2018-07-13  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* lib/gdbserver-support.exp (gdbserver_start): Expect for the
+	message "No address associated with hostname" when gdbserver
+	cannot resolve the hostname.
+
 2018-07-12  Philippe Waroquiers  <philippe.waroquiers@skynet.be>
 
 	* gdb.threads/pthreads.exp: Test qcs FLAG arguments.

gdb/testsuite/lib/gdbserver-support.exp

@@ -326,7 +326,7 @@ proc gdbserver_start { options arguments } {
 		    continue
 		}
 	    }
-	    -re ".*: cannot resolve name: Name or service not known\r\n" {
+	    -re ".*: cannot resolve name: \(No address associated with hostname|Name or service not known\)\r\n" {
 		error "gdbserver cannot resolve name."
 	    }
 	    timeout {