Add missing build requirement libyajl-devel for SUSE distributions

Icinga 2.2.0 doesn't build on SUSE platforms unless the build
requirement libyajl-devel was added.

fixes #7741

Signed-off-by: Gunnar Beutner <gunnar.beutner@netways.de>

icinga2.spec

@@ -84,6 +84,7 @@ Group:        Applications/System
 PreReq:        permissions
 Provides:      monitoring_daemon
 Recommends:    monitoring-plugins
+BuildRequires: libyajl-devel >= 2
 %endif
 BuildRequires: openssl-devel
 BuildRequires: gcc-c++