Make SymlinkTreeStep only mkdirs(p) once for each p
Make SymlinkTreeStep only mkdirs(p) once for each p

Summary: ^^^

Test Plan: CI

Reviewed By: marcinkosiba

fbshipit-source-id: 065d622

SeleniumHQ/buck,shybovycha/buck,ilya-klyuchnikov/buck,marcinkwiatkowski/buck,k21/buck,Addepar/buck,JoelMarcey/buck,clonetwin26/buck,rmaz/buck,clonetwin26/buck,zhan-xiong/buck,nguyentruongtho/buck,clonetwin26/buck,facebook/buck,romanoid/buck,rmaz/buck,romanoid/buck,SeleniumHQ/buck,rmaz/buck,zhan-xiong/buck,dsyang/buck,robbertvanginkel/buck,robbertvanginkel/buck,romanoid/buck,marcinkwiatkowski/buck,Addepar/buck,zpao/buck,marcinkwiatkowski/buck,shybovycha/buck,Addepar/buck,nguyentruongtho/buck,shs96c/buck,romanoid/buck,romanoid/buck,robbertvanginkel/buck,dsyang/buck,dsyang/buck,dsyang/buck,k21/buck,zpao/buck,LegNeato/buck,facebook/buck,kageiit/buck,k21/buck,romanoid/buck,JoelMarcey/buck,brettwooldridge/buck,kageiit/buck,LegNeato/buck,marcinkwiatkowski/buck,rmaz/buck,marcinkwiatkowski/buck,robbertvanginkel/buck,ilya-klyuchnikov/buck,rmaz/buck,k21/buck,LegNeato/buck,zhan-xiong/buck,LegNeato/buck,facebook/buck,brettwooldridge/buck,shs96c/buck,Addepar/buck,SeleniumHQ/buck,romanoid/buck,clonetwin26/buck,SeleniumHQ/buck,nguyentruongtho/buck,facebook/buck,SeleniumHQ/buck,brettwooldridge/buck,Addepar/buck,Addepar/buck,JoelMarcey/buck,SeleniumHQ/buck,brettwooldridge/buck,shybovycha/buck,ilya-klyuchnikov/buck,robbertvanginkel/buck,LegNeato/buck,rmaz/buck,shybovycha/buck,JoelMarcey/buck,ilya-klyuchnikov/buck,clonetwin26/buck,zhan-xiong/buck,SeleniumHQ/buck,marcinkwiatkowski/buck,ilya-klyuchnikov/buck,SeleniumHQ/buck,shybovycha/buck,kageiit/buck,facebook/buck,robbertvanginkel/buck,ilya-klyuchnikov/buck,dsyang/buck,romanoid/buck,LegNeato/buck,kageiit/buck,JoelMarcey/buck,shybovycha/buck,ilya-klyuchnikov/buck,dsyang/buck,brettwooldridge/buck,clonetwin26/buck,JoelMarcey/buck,shybovycha/buck,marcinkwiatkowski/buck,zhan-xiong/buck,shs96c/buck,brettwooldridge/buck,shs96c/buck,SeleniumHQ/buck,robbertvanginkel/buck,Addepar/buck,clonetwin26/buck,Addepar/buck,shs96c/buck,ilya-klyuchnikov/buck,dsyang/buck,marcinkwiatkowski/buck,ilya-klyuchnikov/buck,shybovycha/buck,k21/buck,k21/buck,ilya-klyuchnikov/buck,zpao/buck,rmaz/buck,zhan-xiong/buck,ilya-klyuchnikov/buck,facebook/buck,LegNeato/buck,brettwooldridge/buck,marcinkwiatkowski/buck,romanoid/buck,zpao/buck,romanoid/buck,LegNeato/buck,brettwooldridge/buck,brettwooldridge/buck,romanoid/buck,SeleniumHQ/buck,Addepar/buck,zhan-xiong/buck,robbertvanginkel/buck,clonetwin26/buck,Addepar/buck,LegNeato/buck,marcinkwiatkowski/buck,shybovycha/buck,shybovycha/buck,clonetwin26/buck,zpao/buck,rmaz/buck,zhan-xiong/buck,JoelMarcey/buck,LegNeato/buck,nguyentruongtho/buck,JoelMarcey/buck,ilya-klyuchnikov/buck,romanoid/buck,zpao/buck,brettwooldridge/buck,k21/buck,k21/buck,SeleniumHQ/buck,zhan-xiong/buck,clonetwin26/buck,SeleniumHQ/buck,rmaz/buck,rmaz/buck,k21/buck,shs96c/buck,shs96c/buck,kageiit/buck,dsyang/buck,nguyentruongtho/buck,shs96c/buck,kageiit/buck,robbertvanginkel/buck,LegNeato/buck,SeleniumHQ/buck,marcinkwiatkowski/buck,kageiit/buck,k21/buck,rmaz/buck,rmaz/buck,nguyentruongtho/buck,shs96c/buck,zhan-xiong/buck,LegNeato/buck,k21/buck,robbertvanginkel/buck,brettwooldridge/buck,shs96c/buck,k21/buck,clonetwin26/buck,zhan-xiong/buck,Addepar/buck,zpao/buck,dsyang/buck,shybovycha/buck,k21/buck,zhan-xiong/buck,dsyang/buck,brettwooldridge/buck,brettwooldridge/buck,shybovycha/buck,ilya-klyuchnikov/buck,zhan-xiong/buck,JoelMarcey/buck,LegNeato/buck,nguyentruongtho/buck,facebook/buck,JoelMarcey/buck,dsyang/buck,robbertvanginkel/buck,shs96c/buck,robbertvanginkel/buck,Addepar/buck,shybovycha/buck,shs96c/buck,dsyang/buck,dsyang/buck,rmaz/buck,marcinkwiatkowski/buck,clonetwin26/buck,robbertvanginkel/buck,marcinkwiatkowski/buck,shs96c/buck,JoelMarcey/buck,JoelMarcey/buck,Addepar/buck,JoelMarcey/buck,clonetwin26/buck,romanoid/buck