Exchange: Register always the client cert if present

EasServerConnection#executeHttpUriRequest can create a new different connection that the
caller connection, because the use of the new cache connection classes. This occurs after
the client registry was registered in the all connection. To avoid that, this change
moves the registration of the client cert to the cache.

Change-Id: If62f99ea81f5951a1d2ee9b692b849cf533507ab
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>