Externalize httpd and sshd thread computation

Move sshd.threads, httpd.maxThreads and database.poolLimit to separate
class. This way default value of poolLimit can be dynamically computed
based on two previously mentioned properties.

Change-Id: I5167c4a42ed5e5a480d0ff4accba490dffa05fd4
Signed-off-by: Dariusz Luksza <dariusz@luksza.org>
diff --git a/Documentation/config-gerrit.txt b/Documentation/config-gerrit.txt
index 359f281..97de8df 100644
--- a/Documentation/config-gerrit.txt
+++ b/Documentation/config-gerrit.txt
@@ -1404,7 +1404,8 @@
 httpd and sshd threads as some request processing code paths may
 need multiple connections.
 +
-Default is 8.
+Default is <<sshd.threads, sshd.threads>>
+ + <<httpd.maxThreads, httpd.maxThreads>> + 2.
 +
 This setting only applies if
 <<database.connectionPool,database.connectionPool>> is true.