ryu/utils: make import_module() reliable
ryu/utils: make import_module() reliable

Signed-off-by: Isaku Yamahata <4b3abd66323411eeceff090ab3754dd766fc4b25@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

John-Lin/ryu,diogommartins/ryu,yamada-h/ryu,John-Lin/ryu,castroflavio/ryu,yamt/ryu,openvapour/ryu,haniehrajabi/ryu,gareging/SDN_Framework,iwaseyusuke/ryu,elahejalalpour/ELRyu,lagopus/ryu-lagopus-ext,muzixing/ryu,Tesi-Luca-Davide/ryu,alanquillin/ryu,umkcdcrg01/ryu_openflow,hisaharu/ryu,Tejas-Subramanya/RYU_MEC,zangree/ryu,yamt/ryu,torufuru/oolhackathon,pichuang/ryu,alyosha1879/ryu,unifycore/ryu,Tejas-Subramanya/RYU_MEC,muzixing/ryu,ysywh/ryu,ntts-clo/ryu,shinpeimuraoka/ryu,diogommartins/ryu,lzppp/mylearning,StephenKing/summerschool-2015-ryu,Zouyiran/ryu,yamt/ryu,osrg/ryu,TakeshiTseng/ryu,fujita/ryu,evanscottgray/ryu,ysywh/ryu,jalilm/ryu,habibiefaried/ryu,alyosha1879/ryu,gopchandani/ryu,umkcdcrg01/ryu_openflow,jazzmes/ryu,gareging/SDN_Framework,openvapour/ryu,osrg/ryu,zangree/ryu,fkakuma/ryu,sivaramakrishnansr/ryu,shinpeimuraoka/ryu,jazzmes/ryu,diogommartins/ryu,StephenKing/summerschool-2015-ryu,zyq001/ryu,Tesi-Luca-Davide/ryu,StephenKing/ryu,elahejalalpour/ELRyu,OpenState-SDN/ryu,habibiefaried/ryu,openvapour/ryu,mikhaelharswanto/ryu,gareging/SDN_Framework,darjus-amzn/ryu,zangree/ryu,torufuru/oolhackathon,ynkjm/ryu,o3project/ryu-oe,OpenState-SDN/ryu,elahejalalpour/ELRyu,darjus-amzn/ryu,alanquillin/ryu,zyq001/ryu,iwaseyusuke/ryu,elahejalalpour/ELRyu,takahashiminoru/ryu,fujita/ryu,lsqtongxin/ryu,jalilm/ryu,sivaramakrishnansr/ryu,ntts-clo/mld-ryu,zangree/ryu,zangree/ryu,ttsubo/ryu,o3project/ryu-oe,haniehrajabi/ryu,pichuang/ryu,zyq001/ryu,Tesi-Luca-Davide/ryu,Tesi-Luca-Davide/ryu,StephenKing/ryu,muzixing/ryu,alanquillin/ryu,fujita/ryu,alyosha1879/ryu,hisaharu/ryu,evanscottgray/ryu,lzppp/mylearning,jkoelker/ryu,ttsubo/ryu,yamada-h/ryu,TakeshiTseng/ryu,osrg/ryu,jalilm/ryu,lzppp/mylearning,diogommartins/ryu,alanquillin/ryu,ntts-clo/mld-ryu,takahashiminoru/ryu,Tejas-Subramanya/RYU_MEC,StephenKing/summerschool-2015-ryu,habibiefaried/ryu,darjus-amzn/ryu,elahejalalpour/ELRyu,ysywh/ryu,castroflavio/ryu,osrg/ryu,Zouyiran/ryu,darjus-amzn/ryu,samrussell/ryu,openvapour/ryu,sivaramakrishnansr/ryu,fujita/ryu,fujita/ryu,ntts-clo/ryu,castroflavio/ryu,OpenState-SDN/ryu,umkcdcrg01/ryu_openflow,umkcdcrg01/ryu_openflow,gareging/SDN_Framework,gareging/SDN_Framework,Tejas-Subramanya/RYU_MEC,ykaneko/ryu,fkakuma/ryu,osrg/ryu,Tejas-Subramanya/RYU_MEC,haniehrajabi/ryu,jazzmes/ryu,pichuang/ryu,zyq001/ryu,ynkjm/ryu,jalilm/ryu,lsqtongxin/ryu,ysywh/ryu,OpenState-SDN/ryu,torufuru/oolhackathon,jalilm/ryu,citrix-openstack-build/ryu,shinpeimuraoka/ryu,diogommartins/ryu,pichuang/ryu,shinpeimuraoka/ryu,Zouyiran/ryu,torufuru/OFPatchPanel,gopchandani/ryu,torufuru/OFPatchPanel,mikhaelharswanto/ryu,TakeshiTseng/ryu,fkakuma/ryu,Zouyiran/ryu,ynkjm/ryu,sivaramakrishnansr/ryu,lzppp/mylearning,zyq001/ryu,shinpeimuraoka/ryu,habibiefaried/ryu,TakeshiTseng/ryu,StephenKing/ryu,lagopus/ryu-lagopus-ext,alanquillin/ryu,Zouyiran/ryu,habibiefaried/ryu,ttsubo/ryu,citrix-openstack/build-ryu,StephenKing/ryu,unifycore/ryu,hisaharu/ryu,alyosha1879/ryu,ysywh/ryu,yamt/ryu,pichuang/ryu,John-Lin/ryu,evanscottgray/ryu,lagopus/ryu-lagopus-ext,darjus-amzn/ryu,takahashiminoru/ryu,takahashiminoru/ryu,Tesi-Luca-Davide/ryu,haniehrajabi/ryu,John-Lin/ryu,fkakuma/ryu,ttsubo/ryu,StephenKing/ryu,samrussell/ryu,jkoelker/ryu,ttsubo/ryu,lagopus/ryu-lagopus-ext,hisaharu/ryu,iwaseyusuke/ryu,iwaseyusuke/ryu,lzppp/mylearning,iwaseyusuke/ryu,StephenKing/summerschool-2015-ryu,haniehrajabi/ryu,muzixing/ryu,StephenKing/summerschool-2015-ryu,gopchandani/ryu,lsqtongxin/ryu,openvapour/ryu,gopchandani/ryu,fkakuma/ryu,lsqtongxin/ryu,muzixing/ryu,jkoelker/ryu,OpenState-SDN/ryu,ynkjm/ryu,citrix-openstack/build-ryu,TakeshiTseng/ryu,ykaneko/ryu,yamt/ryu,lsqtongxin/ryu,takahashiminoru/ryu,hisaharu/ryu,sivaramakrishnansr/ryu,John-Lin/ryu,umkcdcrg01/ryu_openflow,lagopus/ryu-lagopus-ext,ynkjm/ryu,citrix-openstack-build/ryu,gopchandani/ryu