utilities/runtests: Clear cache for every file tested
utilities/runtests: Clear cache for every file tested

This fixes the bloated memory usage of our test runner, see issue 2585.
It went up to ~450 MB; it doesn't pass 200 MB now. There shouldn't be
any slowdown due to this (and anecdotally, there isn't).

Signed-off-by: Vladimir Perić <d399dc26d470d14134f6e1c9d95dfd4ee7e0798f@gmail.com>

shipci/sympy,Arafatk/sympy,wanglongqi/sympy,ga7g08/sympy,diofant/diofant,oliverlee/sympy,wanglongqi/sympy,wyom/sympy,wanglongqi/sympy,liangjiaxing/sympy,jamesblunt/sympy,sunny94/temp,cswiercz/sympy,Mitchkoens/sympy,Designist/sympy,drufat/sympy,rahuldan/sympy,Designist/sympy,beni55/sympy,mcdaniel67/sympy,Curious72/sympy,jerli/sympy,garvitr/sympy,shipci/sympy,skirpichev/omg,emon10005/sympy,Gadal/sympy,VaibhavAgarwalVA/sympy,moble/sympy,Mitchkoens/sympy,Shaswat27/sympy,AunShiLord/sympy,lidavidm/sympy,Mitchkoens/sympy,jbbskinny/sympy,abhiii5459/sympy,sampadsaha5/sympy,bukzor/sympy,atsao72/sympy,atreyv/sympy,Titan-C/sympy,sahilshekhawat/sympy,AkademieOlympia/sympy,debugger22/sympy,hrashk/sympy,wyom/sympy,mcdaniel67/sympy,jaimahajan1997/sympy,kaichogami/sympy,garvitr/sympy,Vishluck/sympy,Titan-C/sympy,kevalds51/sympy,pbrady/sympy,toolforger/sympy,iamutkarshtiwari/sympy,oliverlee/sympy,sahmed95/sympy,cswiercz/sympy,chaffra/sympy,maniteja123/sympy,Gadal/sympy,hargup/sympy,bukzor/sympy,sampadsaha5/sympy,AunShiLord/sympy,amitjamadagni/sympy,cccfran/sympy,chaffra/sympy,MechCoder/sympy,asm666/sympy,dqnykamp/sympy,atreyv/sympy,jaimahajan1997/sympy,ahhda/sympy,drufat/sympy,Arafatk/sympy,kevalds51/sympy,debugger22/sympy,sunny94/temp,meghana1995/sympy,shikil/sympy,Titan-C/sympy,sahmed95/sympy,ga7g08/sympy,grevutiu-gabriel/sympy,lindsayad/sympy,madan96/sympy,bukzor/sympy,Curious72/sympy,sahmed95/sympy,cccfran/sympy,sahilshekhawat/sympy,MridulS/sympy,aktech/sympy,iamutkarshtiwari/sympy,abloomston/sympy,kmacinnis/sympy,vipulroxx/sympy,moble/sympy,ahhda/sympy,ga7g08/sympy,srjoglekar246/sympy,liangjiaxing/sympy,abhiii5459/sympy,kumarkrishna/sympy,AunShiLord/sympy,pbrady/sympy,pandeyadarsh/sympy,debugger22/sympy,MechCoder/sympy,maniteja123/sympy,beni55/sympy,skidzo/sympy,MridulS/sympy,aktech/sympy,sampadsaha5/sympy,Gadal/sympy,shipci/sympy,liangjiaxing/sympy,Curious72/sympy,kevalds51/sympy,asm666/sympy,hrashk/sympy,postvakje/sympy,jamesblunt/sympy,farhaanbukhsh/sympy,kumarkrishna/sympy,mcdaniel67/sympy,madan96/sympy,pandeyadarsh/sympy,lindsayad/sympy,mafiya69/sympy,Davidjohnwilson/sympy,souravsingh/sympy,garvitr/sympy,shikil/sympy,sahilshekhawat/sympy,emon10005/sympy,VaibhavAgarwalVA/sympy,flacjacket/sympy,cccfran/sympy,jaimahajan1997/sympy,hargup/sympy,jbbskinny/sympy,kaushik94/sympy,Sumith1896/sympy,toolforger/sympy,aktech/sympy,kaichogami/sympy,VaibhavAgarwalVA/sympy,maniteja123/sympy,AkademieOlympia/sympy,ahhda/sympy,yukoba/sympy,kaushik94/sympy,postvakje/sympy,mafiya69/sympy,Shaswat27/sympy,hrashk/sympy,kmacinnis/sympy,skidzo/sympy,chaffra/sympy,amitjamadagni/sympy,yashsharan/sympy,shikil/sympy,Sumith1896/sympy,Sumith1896/sympy,yashsharan/sympy,souravsingh/sympy,kumarkrishna/sympy,vipulroxx/sympy,jerli/sympy,madan96/sympy,sunny94/temp,abloomston/sympy,lindsayad/sympy,ChristinaZografou/sympy,souravsingh/sympy,ChristinaZografou/sympy,farhaanbukhsh/sympy,jbbskinny/sympy,Vishluck/sympy,toolforger/sympy,iamutkarshtiwari/sympy,yukoba/sympy,atsao72/sympy,Designist/sympy,abloomston/sympy,oliverlee/sympy,saurabhjn76/sympy,moble/sympy,Vishluck/sympy,pbrady/sympy,jamesblunt/sympy,postvakje/sympy,Davidjohnwilson/sympy,yukoba/sympy,ChristinaZografou/sympy,mafiya69/sympy,kaichogami/sympy,wyom/sympy,dqnykamp/sympy,atreyv/sympy,farhaanbukhsh/sympy,skidzo/sympy,asm666/sympy,atsao72/sympy,jerli/sympy,lidavidm/sympy,dqnykamp/sympy,kmacinnis/sympy,kaushik94/sympy,meghana1995/sympy,saurabhjn76/sympy,MechCoder/sympy,AkademieOlympia/sympy,rahuldan/sympy,lidavidm/sympy,MridulS/sympy,emon10005/sympy,abhiii5459/sympy,pandeyadarsh/sympy,Arafatk/sympy,saurabhjn76/sympy,Shaswat27/sympy,beni55/sympy,grevutiu-gabriel/sympy,cswiercz/sympy,meghana1995/sympy,grevutiu-gabriel/sympy,Davidjohnwilson/sympy,vipulroxx/sympy,hargup/sympy,yashsharan/sympy,rahuldan/sympy,drufat/sympy