Summary:
This change:
Moves some opts sanitizing logic into function `sanitizeopts`
Adds checks for `limit` being a positive integer
Uses `sanitizeopts` new function in p4seqimport
Adds a test covering `sanitizeopts`
For a high-level overview of p4seqimport, please check https://our.intern.facebook.com/intern/wiki/IDI/p4seqimport/
Differential Revision: D7035217
fbshipit-source-id: cd677fb254ff83d123673d51a1c682639de08a30
