fix rhel dockerfiles for std|ent packaging

Author: gsmolk

Diff for: packaging/Dockerfiles/Dockerfile-rhel_7

@@ -5,3 +5,5 @@ RUN yum install -y tar wget yum-utils
 RUN yum install -y gcc make perl libicu-devel glibc-devel
 RUN yum install -y git
 RUN yum upgrade -y
+RUN yum install -y http://mirror.centos.org/centos/7/os/x86_64/Packages/bison-3.0.4-2.el7.x86_64.rpm
+RUN yum install -y http://mirror.centos.org/centos/7/os/x86_64/Packages/flex-2.5.37-6.el7.x86_64.rpm

Diff for: packaging/Dockerfiles/Dockerfile-rhel_8

@@ -3,3 +3,5 @@ RUN yum install -y tar wget rpm-build yum-utils
 RUN yum install -y gcc make perl libicu-devel glibc-devel
 RUN yum install -y git
 RUN yum upgrade -y
+RUN yum install -y http://mirror.centos.org/centos/8/AppStream/x86_64/os/Packages/bison-3.0.4-10.el8.x86_64.rpm
+RUN yum install -y http://mirror.centos.org/centos/8/AppStream/x86_64/os/Packages/flex-2.6.1-9.el8.x86_64.rpm