Factor out stub jar creation in `MirrorTest`
Factor out stub jar creation in `MirrorTest`

Summary:
I'm getting ready to introduce a new way of creating ABI jars, and I'd like
to be able to roll it out while keeping the old way. This commit factors out
the part of the test code that actually creates the stubs, so that I can easily
parameterize this test and run it on both implementations.

Test Plan: Unit tests

Reviewed By: asp2insp

fbshipit-source-id: 2a63ae1

sdwilsh/buck,dsyang/buck,k21/buck,shybovycha/buck,facebook/buck,LegNeato/buck,ilya-klyuchnikov/buck,davido/buck,romanoid/buck,rmaz/buck,clonetwin26/buck,marcinkwiatkowski/buck,marcinkwiatkowski/buck,justinmuller/buck,JoelMarcey/buck,LegNeato/buck,nguyentruongtho/buck,rmaz/buck,justinmuller/buck,JoelMarcey/buck,daedric/buck,grumpyjames/buck,dsyang/buck,JoelMarcey/buck,shybovycha/buck,clonetwin26/buck,grumpyjames/buck,zhan-xiong/buck,LegNeato/buck,justinmuller/buck,rmaz/buck,marcinkwiatkowski/buck,darkforestzero/buck,facebook/buck,clonetwin26/buck,dsyang/buck,romanoid/buck,shs96c/buck,dsyang/buck,SeleniumHQ/buck,LegNeato/buck,JoelMarcey/buck,sdwilsh/buck,vschs007/buck,grumpyjames/buck,darkforestzero/buck,shybovycha/buck,vschs007/buck,grumpyjames/buck,darkforestzero/buck,daedric/buck,k21/buck,sdwilsh/buck,dsyang/buck,zhan-xiong/buck,kageiit/buck,justinmuller/buck,ilya-klyuchnikov/buck,dsyang/buck,dsyang/buck,robbertvanginkel/buck,Addepar/buck,Addepar/buck,ilya-klyuchnikov/buck,zhan-xiong/buck,SeleniumHQ/buck,shybovycha/buck,LegNeato/buck,brettwooldridge/buck,shybovycha/buck,Addepar/buck,daedric/buck,Addepar/buck,clonetwin26/buck,romanoid/buck,robbertvanginkel/buck,dsyang/buck,justinmuller/buck,justinmuller/buck,SeleniumHQ/buck,shybovycha/buck,k21/buck,zhan-xiong/buck,shybovycha/buck,marcinkwiatkowski/buck,rmaz/buck,romanoid/buck,sdwilsh/buck,Addepar/buck,darkforestzero/buck,zpao/buck,shybovycha/buck,robbertvanginkel/buck,ilya-klyuchnikov/buck,nguyentruongtho/buck,shs96c/buck,kageiit/buck,darkforestzero/buck,zhan-xiong/buck,darkforestzero/buck,vschs007/buck,brettwooldridge/buck,SeleniumHQ/buck,kageiit/buck,vschs007/buck,Addepar/buck,SeleniumHQ/buck,davido/buck,justinmuller/buck,zpao/buck,vschs007/buck,clonetwin26/buck,rmaz/buck,sdwilsh/buck,davido/buck,shs96c/buck,SeleniumHQ/buck,marcinkwiatkowski/buck,dsyang/buck,LegNeato/buck,shs96c/buck,rmaz/buck,romanoid/buck,Addepar/buck,romanoid/buck,clonetwin26/buck,kageiit/buck,ilya-klyuchnikov/buck,clonetwin26/buck,JoelMarcey/buck,robbertvanginkel/buck,sdwilsh/buck,marcinkwiatkowski/buck,daedric/buck,facebook/buck,sdwilsh/buck,daedric/buck,shs96c/buck,shs96c/buck,romanoid/buck,daedric/buck,brettwooldridge/buck,daedric/buck,vschs007/buck,marcinkwiatkowski/buck,sdwilsh/buck,LegNeato/buck,k21/buck,justinmuller/buck,sdwilsh/buck,nguyentruongtho/buck,darkforestzero/buck,robbertvanginkel/buck,Addepar/buck,ilya-klyuchnikov/buck,davido/buck,zhan-xiong/buck,dsyang/buck,zpao/buck,dsyang/buck,k21/buck,k21/buck,daedric/buck,brettwooldridge/buck,darkforestzero/buck,facebook/buck,davido/buck,davido/buck,k21/buck,SeleniumHQ/buck,Addepar/buck,darkforestzero/buck,robbertvanginkel/buck,darkforestzero/buck,ilya-klyuchnikov/buck,zhan-xiong/buck,zhan-xiong/buck,LegNeato/buck,k21/buck,sdwilsh/buck,LegNeato/buck,rmaz/buck,shs96c/buck,daedric/buck,JoelMarcey/buck,SeleniumHQ/buck,Addepar/buck,romanoid/buck,k21/buck,facebook/buck,SeleniumHQ/buck,brettwooldridge/buck,daedric/buck,rmaz/buck,justinmuller/buck,shs96c/buck,JoelMarcey/buck,LegNeato/buck,zhan-xiong/buck,daedric/buck,davido/buck,clonetwin26/buck,JoelMarcey/buck,marcinkwiatkowski/buck,brettwooldridge/buck,vschs007/buck,brettwooldridge/buck,Addepar/buck,brettwooldridge/buck,zpao/buck,SeleniumHQ/buck,clonetwin26/buck,daedric/buck,ilya-klyuchnikov/buck,brettwooldridge/buck,zhan-xiong/buck,brettwooldridge/buck,davido/buck,justinmuller/buck,robbertvanginkel/buck,darkforestzero/buck,davido/buck,brettwooldridge/buck,shybovycha/buck,zhan-xiong/buck,romanoid/buck,grumpyjames/buck,marcinkwiatkowski/buck,romanoid/buck,vschs007/buck,shs96c/buck,robbertvanginkel/buck,Addepar/buck,facebook/buck,grumpyjames/buck,k21/buck,davido/buck,grumpyjames/buck,shs96c/buck,SeleniumHQ/buck,sdwilsh/buck,darkforestzero/buck,ilya-klyuchnikov/buck,LegNeato/buck,k21/buck,romanoid/buck,rmaz/buck,grumpyjames/buck,clonetwin26/buck,daedric/buck,shybovycha/buck,davido/buck,nguyentruongtho/buck,zpao/buck,vschs007/buck,robbertvanginkel/buck,sdwilsh/buck,JoelMarcey/buck,darkforestzero/buck,brettwooldridge/buck,brettwooldridge/buck,robbertvanginkel/buck,ilya-klyuchnikov/buck,ilya-klyuchnikov/buck,Addepar/buck,zhan-xiong/buck,kageiit/buck,marcinkwiatkowski/buck,rmaz/buck,JoelMarcey/buck,rmaz/buck,ilya-klyuchnikov/buck,k21/buck,grumpyjames/buck,robbertvanginkel/buck,zpao/buck,shs96c/buck,romanoid/buck,ilya-klyuchnikov/buck,shybovycha/buck,grumpyjames/buck,zhan-xiong/buck,grumpyjames/buck,vschs007/buck,justinmuller/buck,vschs007/buck,rmaz/buck,vschs007/buck,vschs007/buck,romanoid/buck,shs96c/buck,marcinkwiatkowski/buck,robbertvanginkel/buck,kageiit/buck,justinmuller/buck,zpao/buck,dsyang/buck,davido/buck,robbertvanginkel/buck,kageiit/buck,shybovycha/buck,nguyentruongtho/buck,JoelMarcey/buck,clonetwin26/buck,JoelMarcey/buck,dsyang/buck,marcinkwiatkowski/buck,LegNeato/buck,facebook/buck,justinmuller/buck,shs96c/buck,SeleniumHQ/buck,LegNeato/buck,nguyentruongtho/buck,shybovycha/buck,clonetwin26/buck,sdwilsh/buck,davido/buck,clonetwin26/buck,k21/buck,nguyentruongtho/buck,marcinkwiatkowski/buck,SeleniumHQ/buck,JoelMarcey/buck,grumpyjames/buck,rmaz/buck