[test] Adding Broadcom configuration file test (#1611)

* [test] Adding Broadcom configuration file test

In order to allow SONiC community to check in Broadcom configuration
file directly under device folder. We need to add this test to make
sure the contents of the configuration is compliant with Broadcom
specifications.

* Invoke test from Debian package builder

* Use $() syntax

* Remove the debug echo statement

Author: yxieca

device/arista/x86_64-arista_7260cx3_64/Arista-7260CX3-D108C8/sai.profile

@@ -1 +1 @@
-SAI_INIT_CONFIG_FILE=/etc/bcm/th2-a7260cx3-64-112x50G+8x100G.config.bcm
+SAI_INIT_CONFIG_FILE=/usr/share/sonic/hwsku/th2-a7260cx3-64-112x50G+8x100G.config.bcm