docker.centos: fixed environment and py3 package

Locales changed (again), now it's set to C.utf8.
python36-setuptools was missing, so it was replaced by
python3-setuptools in installscript.  This should fix the issue with
missing yum-config-manager reported by @dschmitz2017

Dockerfile.centos

 FROM centos:latest
 
-ENV LC_ALL en_US.UTF-8
+ENV LC_ALL C.utf8
 
 RUN yum -y install procps
 

install-centos.sh

@@ -11,7 +11,7 @@ echo "Installing remi repo"
 yum -q -y install http://rpms.remirepo.net/enterprise/remi-release-7.rpm
 
 echo "Installing base dependencies"
-yum -q -y install python36 python36-setuptools python36-virtualenv vim git gcc libevent-devel libxml2-devel libxslt-devel mariadb-server mysql-devel patch yum-utils
+yum -q -y install python36 python3-setuptools python3-virtualenv vim git gcc libevent-devel libxml2-devel libxslt-devel mariadb-server mysql-devel patch yum-utils
 
 
 echo "Installing redis"