Fix python imports in gRPC generated python code
Fix python imports in gRPC generated python code

This changes the import style for proto dependencies from a) to b).
a) "import a.b.c as x"
b) "from a.b import c as x"

Using statement a) causes problems when using __init__ files. If module
"a.b" has an __init__.py file which is importing the python generated
grpc code "a.b.d", then we cannot import a module named "a.b.c" because
the module "a.b" does not exist yet. In this case python will throw:
AttributeError: 'module' object has no attribute 'b'

This PR adapts the code to use the same logic as in:
/google/protobuf/compiler/python/python_generator.cc

kumaralokgithub/grpc,donnadionne/grpc,thinkerou/grpc,jtattermusch/grpc,kpayson64/grpc,msmania/grpc,thinkerou/grpc,pszemus/grpc,yang-g/grpc,daniel-j-born/grpc,yang-g/grpc,7anner/grpc,fuchsia-mirror/third_party-grpc,jtattermusch/grpc,firebase/grpc,Vizerai/grpc,sreecha/grpc,msmania/grpc,simonkuang/grpc,jtattermusch/grpc,deepaklukose/grpc,quizlet/grpc,donnadionne/grpc,quizlet/grpc,ejona86/grpc,vsco/grpc,msmania/grpc,muxi/grpc,ctiller/grpc,matt-kwong/grpc,dgquintas/grpc,carl-mastrangelo/grpc,msmania/grpc,dgquintas/grpc,carl-mastrangelo/grpc,baylabs/grpc,pszemus/grpc,PeterFaiman/ruby-grpc-minimal,muxi/grpc,murgatroid99/grpc,deepaklukose/grpc,PeterFaiman/ruby-grpc-minimal,matt-kwong/grpc,ncteisen/grpc,ncteisen/grpc,firebase/grpc,pszemus/grpc,kskalski/grpc,Vizerai/grpc,kumaralokgithub/grpc,geffzhang/grpc,7anner/grpc,nicolasnoble/grpc,ncteisen/grpc,ejona86/grpc,kumaralokgithub/grpc,dgquintas/grpc,thinkerou/grpc,kskalski/grpc,mehrdada/grpc,daniel-j-born/grpc,thinkerou/grpc,donnadionne/grpc,sreecha/grpc,stanley-cheung/grpc,quizlet/grpc,fuchsia-mirror/third_party-grpc,thinkerou/grpc,Crevil/grpc,zhimingxie/grpc,dgquintas/grpc,grpc/grpc,Vizerai/grpc,Crevil/grpc,deepaklukose/grpc,stanley-cheung/grpc,muxi/grpc,grpc/grpc,ncteisen/grpc,ejona86/grpc,Crevil/grpc,adelez/grpc,thinkerou/grpc,kumaralokgithub/grpc,chrisdunelm/grpc,carl-mastrangelo/grpc,dgquintas/grpc,matt-kwong/grpc,sreecha/grpc,muxi/grpc,geffzhang/grpc,msmania/grpc,stanley-cheung/grpc,jboeuf/grpc,deepaklukose/grpc,murgatroid99/grpc,jboeuf/grpc,jtattermusch/grpc,yongni/grpc,firebase/grpc,jboeuf/grpc,ctiller/grpc,vsco/grpc,Crevil/grpc,sreecha/grpc,kpayson64/grpc,pszemus/grpc,carl-mastrangelo/grpc,zhimingxie/grpc,jtattermusch/grpc,ctiller/grpc,kpayson64/grpc,muxi/grpc,daniel-j-born/grpc,sreecha/grpc,adelez/grpc,matt-kwong/grpc,ncteisen/grpc,geffzhang/grpc,baylabs/grpc,ejona86/grpc,MakMukhi/grpc,thinkerou/grpc,muxi/grpc,baylabs/grpc,kskalski/grpc,MakMukhi/grpc,ejona86/grpc,adelez/grpc,nicolasnoble/grpc,vjpai/grpc,kpayson64/grpc,vsco/grpc,ejona86/grpc,vsco/grpc,kskalski/grpc,donnadionne/grpc,daniel-j-born/grpc,PeterFaiman/ruby-grpc-minimal,jboeuf/grpc,kpayson64/grpc,stanley-cheung/grpc,fuchsia-mirror/third_party-grpc,kriswuollett/grpc,MakMukhi/grpc,Vizerai/grpc,kriswuollett/grpc,yang-g/grpc,yongni/grpc,nicolasnoble/grpc,quizlet/grpc,pszemus/grpc,kskalski/grpc,MakMukhi/grpc,yang-g/grpc,donnadionne/grpc,chrisdunelm/grpc,zhimingxie/grpc,Vizerai/grpc,ctiller/grpc,grpc/grpc,stanley-cheung/grpc,nicolasnoble/grpc,msmania/grpc,vjpai/grpc,Vizerai/grpc,chrisdunelm/grpc,baylabs/grpc,murgatroid99/grpc,MakMukhi/grpc,vsco/grpc,vjpai/grpc,vjpai/grpc,firebase/grpc,nicolasnoble/grpc,7anner/grpc,dgquintas/grpc,vsco/grpc,fuchsia-mirror/third_party-grpc,simonkuang/grpc,geffzhang/grpc,Crevil/grpc,kpayson64/grpc,adelez/grpc,nicolasnoble/grpc,carl-mastrangelo/grpc,yongni/grpc,kumaralokgithub/grpc,kumaralokgithub/grpc,kpayson64/grpc,PeterFaiman/ruby-grpc-minimal,ncteisen/grpc,ejona86/grpc,mehrdada/grpc,jtattermusch/grpc,daniel-j-born/grpc,yongni/grpc,thinkerou/grpc,Crevil/grpc,jtattermusch/grpc,simonkuang/grpc,vsco/grpc,pszemus/grpc,PeterFaiman/ruby-grpc-minimal,yongni/grpc,donnadionne/grpc,pszemus/grpc,deepaklukose/grpc,adelez/grpc,simonkuang/grpc,kskalski/grpc,kriswuollett/grpc,vjpai/grpc,matt-kwong/grpc,chrisdunelm/grpc,vjpai/grpc,nicolasnoble/grpc,geffzhang/grpc,zhimingxie/grpc,adelez/grpc,grpc/grpc,7anner/grpc,firebase/grpc,ctiller/grpc,msmania/grpc,geffzhang/grpc,simonkuang/grpc,firebase/grpc,vjpai/grpc,mehrdada/grpc,deepaklukose/grpc,PeterFaiman/ruby-grpc-minimal,yang-g/grpc,donnadionne/grpc,jboeuf/grpc,vjpai/grpc,ctiller/grpc,stanley-cheung/grpc,jboeuf/grpc,zhimingxie/grpc,jboeuf/grpc,chrisdunelm/grpc,kpayson64/grpc,muxi/grpc,muxi/grpc,ncteisen/grpc,yongni/grpc,muxi/grpc,chrisdunelm/grpc,mehrdada/grpc,vjpai/grpc,MakMukhi/grpc,ejona86/grpc,7anner/grpc,quizlet/grpc,Vizerai/grpc,matt-kwong/grpc,dgquintas/grpc,daniel-j-born/grpc,fuchsia-mirror/third_party-grpc,nicolasnoble/grpc,daniel-j-born/grpc,chrisdunelm/grpc,carl-mastrangelo/grpc,firebase/grpc,carl-mastrangelo/grpc,thinkerou/grpc,baylabs/grpc,murgatroid99/grpc,MakMukhi/grpc,zhimingxie/grpc,matt-kwong/grpc,mehrdada/grpc,vjpai/grpc,sreecha/grpc,jboeuf/grpc,pszemus/grpc,fuchsia-mirror/third_party-grpc,adelez/grpc,Vizerai/grpc,jtattermusch/grpc,carl-mastrangelo/grpc,mehrdada/grpc,quizlet/grpc,chrisdunelm/grpc,firebase/grpc,7anner/grpc,muxi/grpc,dgquintas/grpc,kumaralokgithub/grpc,carl-mastrangelo/grpc,jtattermusch/grpc,baylabs/grpc,fuchsia-mirror/third_party-grpc,adelez/grpc,pszemus/grpc,grpc/grpc,MakMukhi/grpc,kriswuollett/grpc,jboeuf/grpc,Vizerai/grpc,kumaralokgithub/grpc,donnadionne/grpc,sreecha/grpc,ejona86/grpc,dgquintas/grpc,msmania/grpc,sreecha/grpc,ctiller/grpc,muxi/grpc,yang-g/grpc,jtattermusch/grpc,PeterFaiman/ruby-grpc-minimal,ejona86/grpc,mehrdada/grpc,grpc/grpc,stanley-cheung/grpc,thinkerou/grpc,stanley-cheung/grpc,quizlet/grpc,stanley-cheung/grpc,mehrdada/grpc,7anner/grpc,carl-mastrangelo/grpc,msmania/grpc,jboeuf/grpc,stanley-cheung/grpc,mehrdada/grpc,murgatroid99/grpc,carl-mastrangelo/grpc,geffzhang/grpc,kriswuollett/grpc,deepaklukose/grpc,ejona86/grpc,yang-g/grpc,chrisdunelm/grpc,murgatroid99/grpc,grpc/grpc,ctiller/grpc,kpayson64/grpc,sreecha/grpc,yang-g/grpc,baylabs/grpc,zhimingxie/grpc,murgatroid99/grpc,jboeuf/grpc,ncteisen/grpc,Vizerai/grpc,yongni/grpc,kriswuollett/grpc,thinkerou/grpc,kriswuollett/grpc,nicolasnoble/grpc,deepaklukose/grpc,vsco/grpc,dgquintas/grpc,murgatroid99/grpc,firebase/grpc,7anner/grpc,kskalski/grpc,muxi/grpc,vjpai/grpc,baylabs/grpc,adelez/grpc,nicolasnoble/grpc,stanley-cheung/grpc,ncteisen/grpc,donnadionne/grpc,jtattermusch/grpc,murgatroid99/grpc,vsco/grpc,murgatroid99/grpc,donnadionne/grpc,Vizerai/grpc,grpc/grpc,PeterFaiman/ruby-grpc-minimal,sreecha/grpc,ctiller/grpc,simonkuang/grpc,firebase/grpc,ejona86/grpc,sreecha/grpc,simonkuang/grpc,simonkuang/grpc,stanley-cheung/grpc,daniel-j-born/grpc,grpc/grpc,quizlet/grpc,yang-g/grpc,PeterFaiman/ruby-grpc-minimal,zhimingxie/grpc,yongni/grpc,pszemus/grpc,carl-mastrangelo/grpc,ncteisen/grpc,Crevil/grpc,firebase/grpc,jboeuf/grpc,geffzhang/grpc,mehrdada/grpc,ctiller/grpc,donnadionne/grpc,fuchsia-mirror/third_party-grpc,simonkuang/grpc,daniel-j-born/grpc,mehrdada/grpc,quizlet/grpc,chrisdunelm/grpc,nicolasnoble/grpc,dgquintas/grpc,yongni/grpc,vjpai/grpc,PeterFaiman/ruby-grpc-minimal,kriswuollett/grpc,sreecha/grpc,kumaralokgithub/grpc,chrisdunelm/grpc,matt-kwong/grpc,jtattermusch/grpc,grpc/grpc,pszemus/grpc,thinkerou/grpc,fuchsia-mirror/third_party-grpc,Crevil/grpc,deepaklukose/grpc,pszemus/grpc,grpc/grpc,kskalski/grpc,baylabs/grpc,kpayson64/grpc,kskalski/grpc,donnadionne/grpc,kriswuollett/grpc,ncteisen/grpc,Crevil/grpc,kpayson64/grpc,ctiller/grpc,grpc/grpc,fuchsia-mirror/third_party-grpc,zhimingxie/grpc,mehrdada/grpc,ctiller/grpc,geffzhang/grpc,ncteisen/grpc,matt-kwong/grpc,nicolasnoble/grpc,MakMukhi/grpc,7anner/grpc,firebase/grpc