Tests: added proxy_timeout in mail tests.

Default proxy_timeout in mail proxy is 24h, so if nginx shutdown after a test
waits for the timeout to expire for some reason, this may take a while
and hard to diagnose.
diff --git a/mail_error_log.t b/mail_error_log.t
index a563802..5369d8b 100644
--- a/mail_error_log.t
+++ b/mail_error_log.t
@@ -44,6 +44,7 @@
 }
 
 mail {
+    proxy_timeout  15s;
     auth_http  http://127.0.0.1:8080/mail/auth;
 
     server {
diff --git a/mail_imap.t b/mail_imap.t
index da9e7f8..c9b8b4c 100644
--- a/mail_imap.t
+++ b/mail_imap.t
@@ -38,6 +38,7 @@
 
 mail {
     proxy_pass_error_message  on;
+    proxy_timeout  15s;
     auth_http  http://127.0.0.1:8080/mail/auth;
 
     server {
diff --git a/mail_imap_ssl.t b/mail_imap_ssl.t
index 2089a7f..cce45f1 100644
--- a/mail_imap_ssl.t
+++ b/mail_imap_ssl.t
@@ -46,6 +46,7 @@
 
 mail {
     proxy_pass_error_message  on;
+    proxy_timeout  15s;
     auth_http  http://127.0.0.1:8080/mail/auth;
     auth_http_pass_client_cert on;
 
diff --git a/mail_pop3.t b/mail_pop3.t
index 538acb6..e64f3cb 100644
--- a/mail_pop3.t
+++ b/mail_pop3.t
@@ -38,6 +38,7 @@
 
 mail {
     proxy_pass_error_message  on;
+    proxy_timeout  15s;
     auth_http  http://127.0.0.1:8080/mail/auth;
 
     server {
diff --git a/mail_proxy_protocol.t b/mail_proxy_protocol.t
index 73cd720..2a7d54a 100644
--- a/mail_proxy_protocol.t
+++ b/mail_proxy_protocol.t
@@ -39,6 +39,7 @@
 
 mail {
     proxy_pass_error_message  on;
+    proxy_timeout             15s;
     proxy_smtp_auth           on;
     proxy_protocol            on;
     auth_http  http://127.0.0.1:8080/mail/auth;
diff --git a/mail_proxy_smtp_auth.t b/mail_proxy_smtp_auth.t
index a713bd3..28ef0fc 100644
--- a/mail_proxy_smtp_auth.t
+++ b/mail_proxy_smtp_auth.t
@@ -39,6 +39,7 @@
 
 mail {
     proxy_pass_error_message  on;
+    proxy_timeout             15s;
     proxy_smtp_auth           on;
     auth_http  http://127.0.0.1:8080/mail/auth;
     smtp_auth  login plain external;
diff --git a/mail_resolver.t b/mail_resolver.t
index 65e2033..6b375d0 100644
--- a/mail_resolver.t
+++ b/mail_resolver.t
@@ -46,6 +46,8 @@
     smtp_auth    none;
     server_name  locahost;
 
+    proxy_timeout 15s;
+
     # prevent useless resend
     resolver_timeout 2s;
 
diff --git a/mail_smtp.t b/mail_smtp.t
index 0e116a1..d6b8347 100644
--- a/mail_smtp.t
+++ b/mail_smtp.t
@@ -39,6 +39,7 @@
 
 mail {
     proxy_pass_error_message  on;
+    proxy_timeout  15s;
     auth_http  http://127.0.0.1:8080/mail/auth;
     xclient    off;
 
diff --git a/mail_smtp_greeting_delay.t b/mail_smtp_greeting_delay.t
index 515dcb8..605c12a 100644
--- a/mail_smtp_greeting_delay.t
+++ b/mail_smtp_greeting_delay.t
@@ -34,6 +34,7 @@
 
 mail {
     proxy_pass_error_message  on;
+    proxy_timeout  15s;
     auth_http  http://127.0.0.1:8080/mail/auth;
     xclient    off;
 
diff --git a/mail_smtp_xclient.t b/mail_smtp_xclient.t
index 3ee861b..71e40ec 100644
--- a/mail_smtp_xclient.t
+++ b/mail_smtp_xclient.t
@@ -36,6 +36,7 @@
 
 mail {
     proxy_pass_error_message  on;
+    proxy_timeout  15s;
     auth_http  http://127.0.0.1:8080/mail/auth;
     xclient    on;
 
diff --git a/worker_shutdown_timeout_mail.t b/worker_shutdown_timeout_mail.t
index 432bbdd..4c6a162 100644
--- a/worker_shutdown_timeout_mail.t
+++ b/worker_shutdown_timeout_mail.t
@@ -40,6 +40,7 @@
 
 mail {
     proxy_pass_error_message  on;
+    proxy_timeout  15s;
     auth_http  http://127.0.0.1:8080/mail/auth;
     xclient    off;