REGTESTS: add minimal CLI "add map" tests

The map_redirect test already tests for "show map", "del map" and
"clear map" but doesn't have any "add map" command. Let's add some
trivial ones involving one regular entry and two other ones added as
payload, checking they are properly returned.
diff --git a/reg-tests/http-rules/map_redirect.vtc b/reg-tests/http-rules/map_redirect.vtc
index c4a2fbe..7f4526a 100644
--- a/reg-tests/http-rules/map_redirect.vtc
+++ b/reg-tests/http-rules/map_redirect.vtc
@@ -161,6 +161,17 @@
     send "show map ${testdir}/map_redirect.map"
     expect ~ "^\\n"
 
+    # add map ${testdir}/map_redirect.map
+    send "add map ${testdir}/map_redirect.map site1_key site1_value"
+    expect ~ "^\\n"
+
+    # add 2 more entries as payload
+    send "add map ${testdir}/map_redirect.map <<\nsite2_key site2_value\nsite3_key site3_value\n"
+    expect ~ "^\\n"
+
+    send "show map ${testdir}/map_redirect.map"
+    expect ~ "^0x[a-f0-9]+ site1_key site1_value\\n0x[a-f0-9]+ site2_key site2_value\\n0x[a-f0-9]+ site3_key site3_value\\n$"
+
     # del map ${testdir}/map_redirect-be.map test1.example.{com,invalid}
     send "del map ${testdir}/map_redirect-be.map test1.example.com"
     expect ~ "^\\n"