Add Random RT number in rt_filter sanity testcase

1]. Instead of using a hard-coded value, randomise RT number
in the range 900000-4294967295
2]. Removing the serial attribute in the ecmp serial testcases

Change-Id: I9e97202a8db91dd404cd822c4425827894f1c937
Merge "Add Random RT number in rt_filter sanity testcase"