Avoid unrecognized content-type message
Avoid unrecognized content-type message

Fixes bug #904473

If the client does not include a Content-type header in its request
(which is normal for e.g. GET and DELETE) then eventlet will pass us
'text/plain'.

Because 'text/plain' isn't one of our supported request content types
we log:

  Unrecognized Content-Type provided in request

This can be an annoying red-herring for people debugging issues.

The reason that eventlet defaults to text/plain is because it uses
the mimetools.Message.gettype() method:

  Message.gettype()
    Return the message type [..] as specified in the Content-Type
    header. If no such header exists, return 'text/plain'.

The wsgiref web server has the same behavior, whereas mod_wsgi will
pass no content-type and twisted will pass an empty string.

Make our code more robust by treating the empty string or text/plain
as if no content-type header was supplied.

Change-Id: Ide117c807db0dc0f5cbe974788b604b5e236800a

imsplitbit/nova,JioCloud/nova_test_latest,vmturbo/nova,cloudbase/nova,cernops/nova,mikalstill/nova,DirectXMan12/nova-hacking,LoHChina/nova,JioCloud/nova,BeyondTheClouds/nova,OpenAcademy-OpenStack/nova-scheduler,thomasem/nova,imsplitbit/nova,j-carpentier/nova,TwinkleChawla/nova,nikesh-mahalka/nova,alexandrucoman/vbox-nova-driver,projectcalico/calico-nova,rahulunair/nova,shail2810/nova,houshengbo/nova_vmware_compute_driver,luogangyi/bcec-nova,NoBodyCam/TftpPxeBootBareMetal,varunarya10/nova_test_latest,mandeepdhami/nova,vmturbo/nova,hanlind/nova,thomasem/nova,ted-gould/nova,yrobla/nova,barnsnake351/nova,cernops/nova,leilihh/nova,sacharya/nova,Metaswitch/calico-nova,jianghuaw/nova,zzicewind/nova,yrobla/nova,varunarya10/nova_test_latest,whitepages/nova,j-carpentier/nova,vmturbo/nova,devoid/nova,raildo/nova,yosshy/nova,angdraug/nova,fnordahl/nova,edulramirez/nova,virtualopensystems/nova,MountainWei/nova,leilihh/novaha,shahar-stratoscale/nova,maheshp/novatest,OpenAcademy-OpenStack/nova-scheduler,NeCTAR-RC/nova,Triv90/Nova,JioCloud/nova_test_latest,watonyweng/nova,SUSE-Cloud/nova,redhat-openstack/nova,Yuriy-Leonov/nova,maelnor/nova,ntt-sic/nova,maoy/zknova,petrutlucian94/nova_dev,devendermishrajio/nova,usc-isi/nova,tealover/nova,sridevikoushik31/openstack,zaina/nova,alaski/nova,Juniper/nova,Brocade-OpenSource/OpenStack-DNRM-Nova,cloudbau/nova,isyippee/nova,dawnpower/nova,rajalokan/nova,vladikr/nova_drafts,adelina-t/nova,mahak/nova,jianghuaw/nova,openstack/nova,takeshineshiro/nova,projectcalico/calico-nova,zhimin711/nova,Yusuke1987/openstack_template,akash1808/nova,ewindisch/nova,tangfeixiong/nova,petrutlucian94/nova_dev,Tehsmash/nova,cloudbase/nova,nikesh-mahalka/nova,orbitfp7/nova,Stavitsky/nova,aristanetworks/arista-ovs-nova,edulramirez/nova,rrader/nova-docker-plugin,shail2810/nova,iuliat/nova,joker946/nova,shahar-stratoscale/nova,maheshp/novatest,rrader/nova-docker-plugin,cloudbase/nova-virtualbox,whitepages/nova,qwefi/nova,petrutlucian94/nova,gooddata/openstack-nova,zzicewind/nova,klmitch/nova,jianghuaw/nova,BeyondTheClouds/nova,hanlind/nova,eonpatapon/nova,sridevikoushik31/openstack,klmitch/nova,NeCTAR-RC/nova,sebrandon1/nova,BeyondTheClouds/nova,alaski/nova,dawnpower/nova,tanglei528/nova,JianyuWang/nova,rajalokan/nova,shootstar/novatest,MountainWei/nova,rickerc/nova_audit,sridevikoushik31/nova,fajoy/nova,Juniper/nova,NoBodyCam/TftpPxeBootBareMetal,cloudbase/nova,joker946/nova,leilihh/novaha,tudorvio/nova,cyx1231st/nova,sebrandon1/nova,plumgrid/plumgrid-nova,mgagne/nova,citrix-openstack-build/nova,silenceli/nova,klmitch/nova,alvarolopez/nova,tangfeixiong/nova,eharney/nova,Triv90/Nova,kimjaejoong/nova,noironetworks/nova,eayunstack/nova,Juniper/nova,phenoxim/nova,bigswitch/nova,apporc/nova,maoy/zknova,phenoxim/nova,DirectXMan12/nova-hacking,openstack/nova,mmnelemane/nova,usc-isi/nova,dstroppa/openstack-smartos-nova-grizzly,Triv90/Nova,noironetworks/nova,saleemjaveds/https-github.com-openstack-nova,paulmathews/nova,dims/nova,spring-week-topos/nova-week,sebrandon1/nova,hanlind/nova,berrange/nova,devendermishrajio/nova_test_latest,iuliat/nova,akash1808/nova,viggates/nova,viggates/nova,yatinkumbhare/openstack-nova,zaina/nova,maheshp/novatest,angdraug/nova,sridevikoushik31/nova,virtualopensystems/nova,sridevikoushik31/openstack,shootstar/novatest,Metaswitch/calico-nova,Brocade-OpenSource/OpenStack-DNRM-Nova,maoy/zknova,fnordahl/nova,rajalokan/nova,houshengbo/nova_vmware_compute_driver,petrutlucian94/nova,belmiromoreira/nova,yatinkumbhare/openstack-nova,devendermishrajio/nova,dstroppa/openstack-smartos-nova-grizzly,jeffrey4l/nova,JioCloud/nova,redhat-openstack/nova,double12gzh/nova,tealover/nova,akash1808/nova_test_latest,eharney/nova,rahulunair/nova,gooddata/openstack-nova,mandeepdhami/nova,gspilio/nova,usc-isi/nova,savi-dev/nova,ruslanloman/nova,ruslanloman/nova,Francis-Liu/animated-broccoli,Yuriy-Leonov/nova,LoHChina/nova,qwefi/nova,JianyuWang/nova,sridevikoushik31/nova,paulmathews/nova,Francis-Liu/animated-broccoli,ted-gould/nova,plumgrid/plumgrid-nova,scripnichenko/nova,tudorvio/nova,fajoy/nova,devoid/nova,affo/nova,rickerc/nova_audit,Juniper/nova,spring-week-topos/nova-week,CiscoSystems/nova,savi-dev/nova,savi-dev/nova,alvarolopez/nova,dstroppa/openstack-smartos-nova-grizzly,CCI-MOC/nova,affo/nova,badock/nova,rajalokan/nova,cernops/nova,CloudServer/nova,fajoy/nova,barnsnake351/nova,CCI-MOC/nova,blueboxgroup/nova,jianghuaw/nova,vladikr/nova_drafts,bgxavier/nova,sacharya/nova,badock/nova,gspilio/nova,felixma/nova,paulmathews/nova,CloudServer/nova,TieWei/nova,TwinkleChawla/nova,bgxavier/nova,eayunstack/nova,isyippee/nova,citrix-openstack-build/nova,mikalstill/nova,orbitfp7/nova,belmiromoreira/nova,DirectXMan12/nova-hacking,TieWei/nova,CEG-FYP-OpenStack/scheduler,NewpTone/stacklab-nova,cyx1231st/nova,felixma/nova,ntt-sic/nova,scripnichenko/nova,mikalstill/nova,ewindisch/nova,tanglei528/nova,klmitch/nova,tianweizhang/nova,vmturbo/nova,sridevikoushik31/nova,leilihh/nova,gooddata/openstack-nova,bclau/nova,mmnelemane/no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