TestHelper: Remove paths added to sys.path
TestHelper: Remove paths added to sys.path

When running tests, we need to include the directory fo the test file
in the path so that it can be imported easily. But this causes issues
as th PATH becomes cluttered, and module names may clash.
So, we use the preserve_sys_path context manager.

Fixes https://github.com/coala-analyzer/coala/issues/574

sagark123/coala,meetmangukiya/coala,RJ722/coala,karansingh1559/coala,sils1297/coala,ayushin78/coala,sagark123/coala,CruiseDevice/coala,ManjiriBirajdar/coala,vinc456/coala,Nosferatul/coala,Tanmay28/coala,rimacone/testing2,tltuan/coala,coala-analyzer/coala,kartikeys98/coala,Tanmay28/coala,yland/coala,SambitAcharya/coala,yashLadha/coala,djkonro/coala,mr-karan/coala,MariosPanag/coala,vinc456/coala,Tanmay28/coala,svsn2117/coala,yashtrivedi96/coala,impmihai/coala,Shade5/coala,arafsheikh/coala,arush0311/coala,jayvdb/coala,sagark123/coala,incorrectusername/coala,SanketDG/coala,lonewolf07/coala,dagdaggo/coala,CruiseDevice/coala,sudheesh001/coala,NiklasMM/coala,yland/coala,arjunsinghy96/coala,Tanmay28/coala,scriptnull/coala,djkonro/coala,FeodorFitsner/coala,MattAllmendinger/coala,rimacone/testing2,rimacone/testing2,Tanmay28/coala,NalinG/coala,arush0311/coala,refeed/coala,andreimacavei/coala,arjunsinghy96/coala,Asnelchristian/coala,SambitAcharya/coala,ManjiriBirajdar/coala,nemaniarjun/coala,coala/coala,dagdaggo/coala,impmihai/coala,abhiroyg/coala,stevemontana1980/coala,netman92/coala,djkonro/coala,Tanmay28/coala,aptrishu/coala,yashLadha/coala,shreyans800755/coala,coala-analyzer/coala,stevemontana1980/coala,rresol/coala,coala-analyzer/coala,Nosferatul/coala,Tanmay28/coala,scottbelden/coala,Uran198/coala,tushar-rishav/coala,NalinG/coala,nemaniarjun/coala,incorrectusername/coala,Balaji2198/coala,aptrishu/coala,FeodorFitsner/coala,svsn2117/coala,tltuan/coala,svsn2117/coala,swatilodha/coala,damngamerz/coala,dagdaggo/coala,d6e/coala,MattAllmendinger/coala,damngamerz/coala,JohnS-01/coala,sophiavanvalkenburg/coala,Shade5/coala,AdeshAtole/coala,swatilodha/coala,RJ722/coala,arush0311/coala,sophiavanvalkenburg/coala,vinc456/coala,shreyans800755/coala,meetmangukiya/coala,FeodorFitsner/coala,rresol/coala,AbdealiJK/coala,yashtrivedi96/coala,Uran198/coala,MariosPanag/coala,sils1297/coala,coala/coala,NalinG/coala,NiklasMM/coala,NiklasMM/coala,meetmangukiya/coala,scottbelden/coala,SambitAcharya/coala,jayvdb/coala,SambitAcharya/coala,Asalle/coala,scottbelden/coala,damngamerz/coala,RJ722/coala,scriptnull/coala,nemaniarjun/coala,lonewolf07/coala,Asalle/coala,scriptnull/coala,Asnelchristian/coala,arjunsinghy96/coala,swatilodha/coala,saurabhiiit/coala,netman92/coala,netman92/coala,NalinG/coala,sudheesh001/coala,tushar-rishav/coala,scriptnull/coala,SambitAcharya/coala,incorrectusername/coala,refeed/coala,tushar-rishav/coala,arafsheikh/coala,aptrishu/coala,Balaji2198/coala,saurabhiiit/coala,yashLadha/coala,SambitAcharya/coala,ManjiriBirajdar/coala,karansingh1559/coala,SambitAcharya/coala,coala/coala,jayvdb/coala,abhiroyg/coala,JohnS-01/coala,d6e/coala,lonewolf07/coala,Uran198/coala,CruiseDevice/coala,scriptnull/coala,arafsheikh/coala,Tanmay28/coala,JohnS-01/coala,Shade5/coala,AbdealiJK/coala,MariosPanag/coala,saurabhiiit/coala,Balaji2198/coala,AbdealiJK/coala,mr-karan/coala,yashtrivedi96/coala,rresol/coala,NalinG/coala,ayushin78/coala,kartikeys98/coala,ayushin78/coala,tltuan/coala,scriptnull/coala,sudheesh001/coala,Nosferatul/coala,SanketDG/coala,mr-karan/coala,stevemontana1980/coala,karansingh1559/coala,Asnelchristian/coala,SanketDG/coala,abhiroyg/coala,impmihai/coala,scriptnull/coala,andreimacavei/coala,kartikeys98/coala,NalinG/coala,sils1297/coala,Asalle/coala,andreimacavei/coala,MattAllmendinger/coala,NalinG/coala,shreyans800755/coala,AdeshAtole/coala,refeed/coala,yland/coala,AdeshAtole/coala,d6e/coala,sophiavanvalkenburg/coala