integration helpers: fix the wait for docker join
integration helpers: fix the wait for docker join

It used to output `[: -eq: unary operator expected` since the grep
command didn't give any output, therefore generating a syntax error.

Signed-off-by: Andrea Luzzardi <442ffe3ffbfd024afcf0b7f8b108d05bca3aae43@gmail.com>

CiaranCostello/swarm,morpheyesh/swarm,joaofnfernandes/docker.github.io,thaJeztah/docker.github.io,gradywang/swarm,jimenez/swarm,megamsys/swarm,aduermael/docker.github.io,u2mejc/swarm,aduermael/docker.github.io,denverdino/docker.github.io,kunalkushwaha/swarm,moxiegirl/swarm,linecheng/swarm,pssahi/swarm,jimenez/swarm,joeuo/docker.github.io,aduermael/docker.github.io,yp-engineering/swarm,ezrasilvera/swarm,iaintshine/swarm,srikalyan/swarm,CodeNow/swarm,mavenugo/swarm,qianzhangxa/swarm,barais/swarm,BSWANG/denverdino.github.io,swarm-hooks/swarm,linecheng/swarm,PeoplePerHour/libswarm,londoncalling/docker.github.io,Aorjoa/swarm,phiroict/docker,yp-engineering/swarm,PeoplePerHour/libswarm,denverdino/denverdino.github.io,bdwill/docker.github.io,troy0820/docker.github.io,docker/docker.github.io,ricca742/swarm,sanscontext/docker.github.io,johnstep/docker.github.io,denverdino/denverdino.github.io,anweiss/docker.github.io,troy0820/docker.github.io,everett-toews/swarm,JimGalasyn/docker.github.io,abronan/swarm,jimmycmh/swarm,JimGalasyn/docker.github.io,shot/swarm,alexisbellido/docker.github.io,FreedomWangLi/swarm,docker-zh/docker.github.io,docker-zh/docker.github.io,jeffjen/swarm,bsmr-docker/swarm,zkcrescent/swarm,ezrasilvera/swarm,christophelec/swarm,jimmyxian/swarm,shin-/docker.github.io,BSWANG/denverdino.github.io,abronan/swarm,shahankhatch/swarm,christophelec/swarm,kunalkushwaha/swarm,Spritekin/swarm,anweiss/docker.github.io,joeuo/docker.github.io,francisbouvier/swarm,cpuguy83/swarm,CodeNow/swarm,jimmyxian/swarm,LuisBosquez/docker.github.io,jzwlqx/denverdino.github.io,atlassian/swarm,joeuo/docker.github.io,shin-/docker.github.io,troy0820/docker.github.io,kyhavlov/swarm,EderRoger/swarm,jdamick/swarm,parapsyche/swarm,ejholmes/swarm,anweiss/docker.github.io,jdamick/swarm,pdevine/swarm,phiroict/docker,xFragger/swarm,shin-/docker.github.io,mgoelzer/swarm,rillig/docker.github.io,menglingwei/denverdino.github.io,docker/docker.github.io,barais/swarm,akerbis/armhf-swarm,FollowMyDev/swarm,danix800/docker.github.io,NunoEdgarGub1/swarm,raoofm/swarm,bsmr-docker/swarm,denverdino/denverdino.github.io,gonkulator/swarm,sanscontext/docker.github.io,kyhavlov/swarm,mrjana/swarm,fugr/swarm,ehazlett/swarm,denverdino/docker.github.io,denverdino/swarm-1,ezrasilvera/SwarmACLs,bpradipt/swarm,swarm-hooks/swarm,aduermael/docker.github.io,jimmycmh/swarm,adouang/swarm,errordeveloper/swarm,bpradipt/swarm,u2mejc/swarm,Aorjoa/swarm,docker-zh/docker.github.io,rillig/docker.github.io,rchicoli/swarm,FollowMyDev/swarm,tranceitionalMynd/swarm,BSWANG/swarm,unodba/swarm,sanscontext/docker.github.io,mrjana/swarm,denverdino/swarm-1,alexisbellido/docker.github.io,cpuguy83/swarm,menglingwei/denverdino.github.io,JimGalasyn/docker.github.io,denverdino/denverdino.github.io,jzwlqx/denverdino.github.io,dnephin/swarm,joaofnfernandes/docker.github.io,bdwill/docker.github.io,thaJeztah/docker.github.io,shin-/docker.github.io,polyverse-security/swarm,docker/docker.github.io,megamsys/swarm,rutulpatel/swarm,sfsmithcha/swarm,JimGalasyn/docker.github.io,ealang/swarm,adouang/swarm,vlajos/swarm,liubin/swarm,docker/docker.github.io,docker-zh/docker.github.io,CiaranCostello/swarm,dims/swarm,phiroict/docker,shubheksha/docker.github.io,shahankhatch/swarm,ehazlett/swarm,ricca742/swarm,liubin/swarm,rchicoli/swarm,BSWANG/denverdino.github.io,snrism/swarm,danix800/docker.github.io,ejholmes/swarm,allencloud/swarm,docker-zh/docker.github.io,denverdino/swarm,sfsmithcha/swarm,rajdeepd/swarm,mgoelzer/swarm,Spritekin/swarm,rancher/swarm,gonkulator/swarm,menglingwei/denverdino.github.io,rajdeepd/swarm,ealang/swarm,iaintshine/swarm,rav121/swarm,denverdino/denverdino.github.io,riuvshin/swarm,gdevillele/docker.github.io,everett-toews/swarm,pdevine/swarm,bdwill/docker.github.io,srikalyan/swarm,therealbill/swarm,rillig/docker.github.io,auzias/swarm,jeffjen/swarm,phiroict/docker,londoncalling/docker.github.io,ch3lo/swarm,affo/swarm,menglingwei/denverdino.github.io,thaJeztah/docker.github.io,johnstep/docker.github.io,ezrasilvera/SwarmACLs,cgvarela/swarm,qianzhangxa/swarm,tangkun75/swarm,EderRoger/swarm,errordeveloper/swarm,menglingwei/denverdino.github.io,denverdino/docker.github.io,xFragger/swarm,BSWANG/denverdino.github.io,joaofnfernandes/docker.github.io,jzwlqx/denverdino.github.io,gdevillele/docker.github.io,moxiegirl/swarm,unodba/swarm,FreedomWangLi/swarm,LuisBosquez/docker.github.io,snrism/swarm,londoncalling/docker.github.io,gdevillele/docker.github.io,londoncalling/docker.github.io,krystism/swarm,jzwlqx/denverdino.github.io,denverdino/docker.github.io,shubheksha/docker.github.io,docker/docker.github.io,auzias/swarm,denverdino/docker.github.io,shot/swarm,shubheksha/docker.github.io,rutulpatel/swarm,tangkun75/swarm,joaofnfernandes/docker.github.io,phiroict/docker,thaJeztah/docker.github.io,johnstep/docker.github.io,resouer/swarm,echupriyanov/swarm,rav121/swarm,francisbouvier/swarm,danix800/docker.github.io,BSWANG/denverdino.github.io,cgvarela/swarm,joaofnfernandes/docker.github.io,anweiss/docker.github.io,MHBauer/swarm,affo/swarm,LukasBacigal/swarm,doronp/swarm,ch3lo/swarm,morpheyesh/swarm,raoofm/swarm,zkcrescent/swarm,joeuo/docker.github.io,polyverse-security/swarm,alexisbellido/docker.github.io,dims/swarm,joeuo/docker.github.io,johnstep/docker.github.io,schmunk42/swarm,schmunk42/swarm,londoncalling/docker.github.io,anweiss/docker.github.io,dnephin/swarm,bdwill/docker.github.io,atlassian/swarm,alexisbellido/docker.github.io,parapsyche/swarm,therealbill/swarm,thaJeztah/docker.github.io,LukasBacigal/swarm,shin-/docker.github.io,shubheksha/docker.github.io,mavenugo/swarm,BSWANG/swarm,fugr/swarm,LuisBosquez/docker.github.io,allencloud/swarm,LuisBosquez/docker.github.io,rancher/swarm,gdevillele/docker.github.io,resouer/swarm,troy0820/docker.github.io,gradywang/swarm,sanscontext/docker.github.io,rillig/docker.github.io,krystism/swarm,alexisbellido/docker.github.io,bdwill/docker.github.io,shubheksha/docker.github.io,doronp/swarm,pssahi/swarm,sanscontext/docker.github.io,beni55/swarm-1,tranceitionalMynd/swarm,NunoEdgarGub1/swarm,vlajos/swarm,denverdino/swarm,danix800/docker.github.io,jay-lau/swarm,akerbis/armhf-swarm,LuisBosquez/docker.github.io,jzwlqx/denverdino.github.io,beni55/swarm-1,riuvshin/swarm,johnstep/docker.github.io,JimGalasyn/docker.github.io,MHBauer/swarm,jay-lau/swarm,echupriyanov/swarm,gdevillele/docker.github.io